The document provides recommendations for safe design and construction of multistorey reinforced concrete buildings based on lessons learned from past earthquakes. Key contributing factors that led to poor performance of buildings during earthquakes are identified and recommendations are provided to address each factor. The main factors discussed are: ignorance of earthquake resistant design codes, soft base soil, soft first stories, structural irregularities, heavy rooftop tanks, lack of seismic design, improper reinforcement detailing, short columns, torsional failures, and pounding between adjacent buildings. Adhering to Indian design codes and accounting for all seismic forces is emphasized.
This report summarizes a site visit to observe the construction of reinforced concrete slabs. Various slab types like one-way slabs, two-way slabs, and sunken slabs were observed. Reinforcement details like bent bars, distribution bars, and concrete cover were seen to match theoretical specifications. Questions about slab design and construction were answered on site. The visit confirmed that theoretical RCC knowledge was being properly implemented in practice.
Self-compacting concrete was developed in Japan in the 1980s to solve problems with inadequate compaction of traditional concrete. It uses a high paste content and superplasticizers to create a concrete that can flow and consolidate under its own weight without vibration. Tests were developed to evaluate properties like filling ability, passing ability, and segregation resistance. Self-compacting concrete provides benefits like easier placement, faster construction, better surface finish, and improved durability. However, it also has higher costs associated with materials and mix design development.
Cement is a binding agent that undergoes hydration when mixed with water. There are various types of cement including ordinary Portland cement (OPC), rapid hardening cement, and sulphate resisting cement. Cement provides early strength through C3S and later strength through C2S. Heat is generated during cement hydration through an exothermic reaction. Proper storing, grading of aggregates, minimizing segregation, and adding admixtures can improve the properties of concrete.
This presentation discusses prefabricated building components. It covers prefabrication systems including large panel systems, frame systems, and slab-column systems. Manufacturing processes are described for various components like roof slabs, floor slabs, waffle slabs, wall panels, shear walls, beams, and columns. Specific component types like floor slabs, waffle slabs, wall panels, and shear walls are explained in more detail. Architectural and structural design aspects of using prefabricated components are also addressed.
This document discusses various concepts related to structural analysis of arches:
1. An arch is a curved girder supported at its ends, allowing only vertical and horizontal displacements for arch action.
2. The general cable theorem relates the horizontal tension and vertical distance from any cable point to the cable chord moment.
3. Arches are classified based on support conditions (3, 2, or 1 hinged) or shape (curved, parabolic, elliptical, polygonal).
4. Horizontal thrust in arches reduces the bending moment and is calculated differently for various arch types (e.g. parabolic) and loading (e.g. UDL).
This document discusses retrofitting of structures. Retrofitting is required when structures are damaged or do not meet current seismic standards. It summarizes various retrofitting techniques such as adding shear walls, infill walls, steel bracing, wall thickening, wing walls, mass reduction, base isolation, and jacketing structural elements. It provides examples of existing retrofitted structures in Gujarat. Retrofitting increases strength and ductility but can reduce space and increase foundation loads. Materials discussed include steel, fiber reinforced polymer, and reinforced concrete.
The document discusses ductility and ductile detailing in reinforced concrete structures. It states that structures should be designed to have lateral strength, deformability, and ductility to resist earthquakes with limited damage and no collapse. Ductility allows structures to develop their full strength through internal force redistribution. Detailing of reinforcement is important to avoid brittle failure and induce ductile behavior by allowing steel to yield in a controlled manner. Shear walls are also discussed as vertical reinforced concrete elements that help structures resist earthquake loads in a ductile manner.
This report summarizes a site visit to observe the construction of reinforced concrete slabs. Various slab types like one-way slabs, two-way slabs, and sunken slabs were observed. Reinforcement details like bent bars, distribution bars, and concrete cover were seen to match theoretical specifications. Questions about slab design and construction were answered on site. The visit confirmed that theoretical RCC knowledge was being properly implemented in practice.
Self-compacting concrete was developed in Japan in the 1980s to solve problems with inadequate compaction of traditional concrete. It uses a high paste content and superplasticizers to create a concrete that can flow and consolidate under its own weight without vibration. Tests were developed to evaluate properties like filling ability, passing ability, and segregation resistance. Self-compacting concrete provides benefits like easier placement, faster construction, better surface finish, and improved durability. However, it also has higher costs associated with materials and mix design development.
Cement is a binding agent that undergoes hydration when mixed with water. There are various types of cement including ordinary Portland cement (OPC), rapid hardening cement, and sulphate resisting cement. Cement provides early strength through C3S and later strength through C2S. Heat is generated during cement hydration through an exothermic reaction. Proper storing, grading of aggregates, minimizing segregation, and adding admixtures can improve the properties of concrete.
This presentation discusses prefabricated building components. It covers prefabrication systems including large panel systems, frame systems, and slab-column systems. Manufacturing processes are described for various components like roof slabs, floor slabs, waffle slabs, wall panels, shear walls, beams, and columns. Specific component types like floor slabs, waffle slabs, wall panels, and shear walls are explained in more detail. Architectural and structural design aspects of using prefabricated components are also addressed.
This document discusses various concepts related to structural analysis of arches:
1. An arch is a curved girder supported at its ends, allowing only vertical and horizontal displacements for arch action.
2. The general cable theorem relates the horizontal tension and vertical distance from any cable point to the cable chord moment.
3. Arches are classified based on support conditions (3, 2, or 1 hinged) or shape (curved, parabolic, elliptical, polygonal).
4. Horizontal thrust in arches reduces the bending moment and is calculated differently for various arch types (e.g. parabolic) and loading (e.g. UDL).
This document discusses retrofitting of structures. Retrofitting is required when structures are damaged or do not meet current seismic standards. It summarizes various retrofitting techniques such as adding shear walls, infill walls, steel bracing, wall thickening, wing walls, mass reduction, base isolation, and jacketing structural elements. It provides examples of existing retrofitted structures in Gujarat. Retrofitting increases strength and ductility but can reduce space and increase foundation loads. Materials discussed include steel, fiber reinforced polymer, and reinforced concrete.
The document discusses ductility and ductile detailing in reinforced concrete structures. It states that structures should be designed to have lateral strength, deformability, and ductility to resist earthquakes with limited damage and no collapse. Ductility allows structures to develop their full strength through internal force redistribution. Detailing of reinforcement is important to avoid brittle failure and induce ductile behavior by allowing steel to yield in a controlled manner. Shear walls are also discussed as vertical reinforced concrete elements that help structures resist earthquake loads in a ductile manner.
This document provides an overview of STAAD.Pro structural analysis software. It discusses the history and development of STAAD.Pro, the types of structures that can be modeled, how to generate models using various tools and methods, assigning properties, loads, and supports, performing analysis and design, and the advantages of STAAD.Pro. In conclusion, STAAD.Pro is widely used in the construction industry for structural design and analysis, though skilled engineers proficient in its use remain in high demand.
Working Stress Method v/s Limit State MethodMachenLink
The document compares the Working Stress Method and Limit State Method for structural design. The Working Stress Method is an elastic, stress-based, deterministic design approach where members are designed to remain in the elastic range using allowable stresses. The Limit State Method is a plastic, strain-based, non-deterministic approach where partial safety factors are used and the material is allowed to yield and enter the plastic zone to reach ultimate strength.
This document is the Indian Standard (Part 1) for earthquake resistant design of structures. It provides general provisions and criteria for assessing earthquake hazards and designing buildings to resist earthquakes. Some key points:
- It defines seismic zones across India based on past earthquake intensities and establishes design response spectra for each zone.
- It provides minimum design forces for normal structures and notes that special structures may require more rigorous site-specific analysis.
- This revision includes changes such as defining design spectra to 6 seconds, specifying the same spectra for all building materials, including temporary structures, and provisions for irregular buildings and masonry infill walls.
- It establishes terminology used in earthquake engineering and references other relevant Indian Standards for
Geopolymer concrete is an innovative, eco-friendly construction material.
It is used as replacement of cement concrete.
In geopolymer concrete cement is not used as a binding material.
Fly ash, silica-fume, or GGBS, along with alkali solution are used as binders.
Concrete permeability is a key factor in its durability. Permeability is affected by water-cement ratio, with lower ratios producing less permeable concrete. Curing also impacts permeability. Proper curing, including moist curing, produces less permeable concrete. Permeability testing involves measuring water flow through a sample over time under pressure. Sulfate attack can occur when sulfates penetrate permeable concrete and form expansive compounds that crack the material. Resistance to sulfates is improved with lower permeability concrete.
1. The document discusses the design and analysis of storage reservoirs and overhead tanks. It covers various types of tanks, design considerations for concrete mixes, crack development remedies, permissible stresses, and reinforcement requirements.
2. Methods for analyzing circular and rectangular tanks are presented. For circular tanks, designs consider rigid versus flexible joints with the base slab. Approximate methods analyze the bottom portion as cantilever and the rest as resisting pressure through horizontal forces.
3. Rectangular tank analysis depends on the length-breadth ratio, treating short walls as bending horizontally between long walls which transfer pressure as tension.
Seismic Analysis of regular & Irregular RCC frame structuresDaanish Zama
This document discusses seismic analysis of regular and irregular reinforced concrete framed buildings. It analyzes 4 building models - a regular 4-story building, a stiffness irregular building with a soft ground story, and two vertically irregular buildings with setbacks on the 3rd floor and 2nd/3rd floors. Static analysis was performed to compare bending moments, shear forces, story drifts, and joint displacements. Results showed irregular buildings experienced higher seismic demands. The regular building performed best, with the single setback building also performing well. Irregular configurations increase seismic effects and should be minimized in design.
1. Masonry structures are vulnerable to earthquake damage due to their brittle nature and weak connections.
2. Common failure modes of masonry buildings during earthquakes include walls tearing apart, shearing off diagonally, and collapsing at corners.
3. Non-destructive testing methods like rebound hammer, ultrasonic pulse velocity, and flat jack tests are used to evaluate the strength of existing masonry structures without damaging them.
The document provides guidelines for repair and rehabilitation of existing reinforced concrete buildings. It discusses causes of concrete deterioration like permeability, aggressive agents, and condition surveys. Non-destructive tests are recommended to evaluate concrete quality, cracking, and corrosion. The approach involves identifying deterioration causes, assessing damage extent, and selecting appropriate repair materials and methods to rehabilitate structures in a systematic and cost-effective manner.
Formwork is a temporary mold used to contain and shape wet concrete until it is cured, and gain sufficient strength to support its own weight. It is commonly made from timber or steel. Formwork must balance requirements like containment, strength, resistance to leakage, accuracy, ease of handling, finish, access for concrete, and economy. It is designed according to factors like the loads it will support, type of structure being built, and materials used. Formwork goes through stages of assembly, concrete placement, and stripping. Proper design, construction, and maintenance of formwork is important to produce high quality, safe concrete structures economically.
This document outlines 8 techniques for repairing cracks in concrete structures: 1) Sealing with epoxies, 2) Routing and sealing, 3) Stitching, 4) External stressing, 5) Overlays, 6) Grouting, 7) Blanketing, and 8) Autogenous healing. Sealing with epoxies involves injecting epoxy compounds into cracks at high pressure. Routing and sealing enlarges cracks and fills them with sealants. Stitching reestablishes tensile strength across major cracks using metal units drilled into crack walls. External stressing closes cracks by applying compression to overcome tensile stresses. Overlays provide a sealed surface for multiple cracks. Grouting is an alternative
STRUCTURE DESIGN REPORT - PREPARED BY 3RD YEAR STUDENTS OF BACHELOR OF ARCHITECTURE FROM INDO GLOBAL COLLEGE OF ARCHITECTURE AFFILIATED WITH I.K. GUJRAL PUNJAB TECHNICAL UNIVERSITY
The document discusses cracks in buildings, including the types, causes, effects, and methods for repairing cracks. It identifies two main types of cracks: structural cracks that could endanger safety, and non-structural cracks caused by factors like moisture, temperature changes, or chemical reactions. Left unaddressed, cracks can accelerate concrete deterioration and carbonation, compromise waterproofing, and affect building appearance and durability. The document outlines various techniques for repairing cracks, such as epoxy injection, routing and sealing, stitching, drilling and plugging, and gravity filling. It emphasizes the importance of both preventing cracks and properly repairing existing cracks to maintain building integrity.
The document discusses the design of footings for structures. It begins by explaining that footings are needed to transfer structural loads from members made of materials like steel and concrete to the underlying soil. It then describes different types of shallow and deep foundations, including spread, strap, combined, and raft footings. The document provides details on designing isolated and combined footings to resist vertical loads and moments based on provisions in IS 456. It also discusses wall footings and combined footings that support multiple columns. In summary, the document covers the purpose of footings, various footing types, and design of isolated and combined footings.
This document discusses column jacketing, which is a method of retrofitting and strengthening existing columns. It involves adding reinforced concrete, steel, or fiber-reinforced polymer around the column. The key steps are preparing the column surface, adding shear keys and reinforcement, applying a bonding agent, and casting the new concrete or installing the jacket. Column jacketing increases the strength and seismic capacity of the column. It improves confinement and increases axial, shear, and foundation load capacity without significant weight addition.
1. Superstructure construction includes column, beam, floor, wall and roof located above ground level. Materials used are timber, steel and concrete.
2. Timber floor construction involves plank wood supported by timber joists and beams. Reinforced concrete uses column and beam construction with formwork, steel bar installation and concrete pouring.
3. Load bearing walls support loads and transfer to foundation, with minimum thickness of one brick. Non-load bearing walls only support own weight and are half brick thickness.
Estimates are important documents that calculate the quantities, rates, and anticipated costs of works involved in a construction project. They help determine approximate construction costs, taxes, rents, materials, labor, and more. A quantity surveyor takes off quantities from drawings and calculates rates and costs. Estimates include preliminary, rough cost, detailed, annual repair, special repair, revised, supplementary, and complete estimates. They provide essential cost information to help plan and budget construction projects.
This document discusses ferrocement, which is a reinforced concrete made of cement mortar and closely spaced steel mesh or rods. It describes the materials used including cement mortar mix, skeleton steel, and steel mesh reinforcement. It outlines the properties of ferrocement such as durability, strength, and flexibility. Finally, it covers the applications, advantages like cost effectiveness, and disadvantages of ferrocement.
This presentation contains IS Concrete mix design method and Basics of Design mix of concrete.It conveys; Objectives of Mix Design ;Grades of Concrete; Nominal Mix and Design Mix; Factors affecting Choice of Mix Design; Methods of Concrete Mix Design; IS Method Of Design.
Civil Technical questions word presentationpremsai05
This consists of various basic civil engineering questions.This can used for screening members in first rounds.The key will be sent to you when u comment and send your mail id
This document provides an overview of STAAD.Pro structural analysis software. It discusses the history and development of STAAD.Pro, the types of structures that can be modeled, how to generate models using various tools and methods, assigning properties, loads, and supports, performing analysis and design, and the advantages of STAAD.Pro. In conclusion, STAAD.Pro is widely used in the construction industry for structural design and analysis, though skilled engineers proficient in its use remain in high demand.
Working Stress Method v/s Limit State MethodMachenLink
The document compares the Working Stress Method and Limit State Method for structural design. The Working Stress Method is an elastic, stress-based, deterministic design approach where members are designed to remain in the elastic range using allowable stresses. The Limit State Method is a plastic, strain-based, non-deterministic approach where partial safety factors are used and the material is allowed to yield and enter the plastic zone to reach ultimate strength.
This document is the Indian Standard (Part 1) for earthquake resistant design of structures. It provides general provisions and criteria for assessing earthquake hazards and designing buildings to resist earthquakes. Some key points:
- It defines seismic zones across India based on past earthquake intensities and establishes design response spectra for each zone.
- It provides minimum design forces for normal structures and notes that special structures may require more rigorous site-specific analysis.
- This revision includes changes such as defining design spectra to 6 seconds, specifying the same spectra for all building materials, including temporary structures, and provisions for irregular buildings and masonry infill walls.
- It establishes terminology used in earthquake engineering and references other relevant Indian Standards for
Geopolymer concrete is an innovative, eco-friendly construction material.
It is used as replacement of cement concrete.
In geopolymer concrete cement is not used as a binding material.
Fly ash, silica-fume, or GGBS, along with alkali solution are used as binders.
Concrete permeability is a key factor in its durability. Permeability is affected by water-cement ratio, with lower ratios producing less permeable concrete. Curing also impacts permeability. Proper curing, including moist curing, produces less permeable concrete. Permeability testing involves measuring water flow through a sample over time under pressure. Sulfate attack can occur when sulfates penetrate permeable concrete and form expansive compounds that crack the material. Resistance to sulfates is improved with lower permeability concrete.
1. The document discusses the design and analysis of storage reservoirs and overhead tanks. It covers various types of tanks, design considerations for concrete mixes, crack development remedies, permissible stresses, and reinforcement requirements.
2. Methods for analyzing circular and rectangular tanks are presented. For circular tanks, designs consider rigid versus flexible joints with the base slab. Approximate methods analyze the bottom portion as cantilever and the rest as resisting pressure through horizontal forces.
3. Rectangular tank analysis depends on the length-breadth ratio, treating short walls as bending horizontally between long walls which transfer pressure as tension.
Seismic Analysis of regular & Irregular RCC frame structuresDaanish Zama
This document discusses seismic analysis of regular and irregular reinforced concrete framed buildings. It analyzes 4 building models - a regular 4-story building, a stiffness irregular building with a soft ground story, and two vertically irregular buildings with setbacks on the 3rd floor and 2nd/3rd floors. Static analysis was performed to compare bending moments, shear forces, story drifts, and joint displacements. Results showed irregular buildings experienced higher seismic demands. The regular building performed best, with the single setback building also performing well. Irregular configurations increase seismic effects and should be minimized in design.
1. Masonry structures are vulnerable to earthquake damage due to their brittle nature and weak connections.
2. Common failure modes of masonry buildings during earthquakes include walls tearing apart, shearing off diagonally, and collapsing at corners.
3. Non-destructive testing methods like rebound hammer, ultrasonic pulse velocity, and flat jack tests are used to evaluate the strength of existing masonry structures without damaging them.
The document provides guidelines for repair and rehabilitation of existing reinforced concrete buildings. It discusses causes of concrete deterioration like permeability, aggressive agents, and condition surveys. Non-destructive tests are recommended to evaluate concrete quality, cracking, and corrosion. The approach involves identifying deterioration causes, assessing damage extent, and selecting appropriate repair materials and methods to rehabilitate structures in a systematic and cost-effective manner.
Formwork is a temporary mold used to contain and shape wet concrete until it is cured, and gain sufficient strength to support its own weight. It is commonly made from timber or steel. Formwork must balance requirements like containment, strength, resistance to leakage, accuracy, ease of handling, finish, access for concrete, and economy. It is designed according to factors like the loads it will support, type of structure being built, and materials used. Formwork goes through stages of assembly, concrete placement, and stripping. Proper design, construction, and maintenance of formwork is important to produce high quality, safe concrete structures economically.
This document outlines 8 techniques for repairing cracks in concrete structures: 1) Sealing with epoxies, 2) Routing and sealing, 3) Stitching, 4) External stressing, 5) Overlays, 6) Grouting, 7) Blanketing, and 8) Autogenous healing. Sealing with epoxies involves injecting epoxy compounds into cracks at high pressure. Routing and sealing enlarges cracks and fills them with sealants. Stitching reestablishes tensile strength across major cracks using metal units drilled into crack walls. External stressing closes cracks by applying compression to overcome tensile stresses. Overlays provide a sealed surface for multiple cracks. Grouting is an alternative
STRUCTURE DESIGN REPORT - PREPARED BY 3RD YEAR STUDENTS OF BACHELOR OF ARCHITECTURE FROM INDO GLOBAL COLLEGE OF ARCHITECTURE AFFILIATED WITH I.K. GUJRAL PUNJAB TECHNICAL UNIVERSITY
The document discusses cracks in buildings, including the types, causes, effects, and methods for repairing cracks. It identifies two main types of cracks: structural cracks that could endanger safety, and non-structural cracks caused by factors like moisture, temperature changes, or chemical reactions. Left unaddressed, cracks can accelerate concrete deterioration and carbonation, compromise waterproofing, and affect building appearance and durability. The document outlines various techniques for repairing cracks, such as epoxy injection, routing and sealing, stitching, drilling and plugging, and gravity filling. It emphasizes the importance of both preventing cracks and properly repairing existing cracks to maintain building integrity.
The document discusses the design of footings for structures. It begins by explaining that footings are needed to transfer structural loads from members made of materials like steel and concrete to the underlying soil. It then describes different types of shallow and deep foundations, including spread, strap, combined, and raft footings. The document provides details on designing isolated and combined footings to resist vertical loads and moments based on provisions in IS 456. It also discusses wall footings and combined footings that support multiple columns. In summary, the document covers the purpose of footings, various footing types, and design of isolated and combined footings.
This document discusses column jacketing, which is a method of retrofitting and strengthening existing columns. It involves adding reinforced concrete, steel, or fiber-reinforced polymer around the column. The key steps are preparing the column surface, adding shear keys and reinforcement, applying a bonding agent, and casting the new concrete or installing the jacket. Column jacketing increases the strength and seismic capacity of the column. It improves confinement and increases axial, shear, and foundation load capacity without significant weight addition.
1. Superstructure construction includes column, beam, floor, wall and roof located above ground level. Materials used are timber, steel and concrete.
2. Timber floor construction involves plank wood supported by timber joists and beams. Reinforced concrete uses column and beam construction with formwork, steel bar installation and concrete pouring.
3. Load bearing walls support loads and transfer to foundation, with minimum thickness of one brick. Non-load bearing walls only support own weight and are half brick thickness.
Estimates are important documents that calculate the quantities, rates, and anticipated costs of works involved in a construction project. They help determine approximate construction costs, taxes, rents, materials, labor, and more. A quantity surveyor takes off quantities from drawings and calculates rates and costs. Estimates include preliminary, rough cost, detailed, annual repair, special repair, revised, supplementary, and complete estimates. They provide essential cost information to help plan and budget construction projects.
This document discusses ferrocement, which is a reinforced concrete made of cement mortar and closely spaced steel mesh or rods. It describes the materials used including cement mortar mix, skeleton steel, and steel mesh reinforcement. It outlines the properties of ferrocement such as durability, strength, and flexibility. Finally, it covers the applications, advantages like cost effectiveness, and disadvantages of ferrocement.
This presentation contains IS Concrete mix design method and Basics of Design mix of concrete.It conveys; Objectives of Mix Design ;Grades of Concrete; Nominal Mix and Design Mix; Factors affecting Choice of Mix Design; Methods of Concrete Mix Design; IS Method Of Design.
Civil Technical questions word presentationpremsai05
This consists of various basic civil engineering questions.This can used for screening members in first rounds.The key will be sent to you when u comment and send your mail id
MULTIPLE CHOICE QUESTIONS for civil engineering students or may be for engine...JASHU JASWANTH
The document discusses various topics related to construction including foundations, bricks, arches, and stairs. It provides multiple choice questions about Raymond piles, queen closer placement, uses of dado, types of footings, placement of foundations, stud placement in partitions, borehole spacing, geophysical testing methods, offset footing placement, identifying brick faces, taper of precast piles, arch components, raft slab projection, soil preparation techniques, suitability of black cotton soil, bridging loose pockets in soil, identifying partial bricks, recommended concrete slump, purpose of purlins, common door types, uses of grillage foundations, defining exterior wall angles, jack arch floor design, and typical rise and going ratios for stairs.
Reinforced concrete is a composite material consisting of concrete and steel reinforcement. François Coignet built the first iron reinforced concrete structure in 1853. Reinforced concrete uses the strengths of both materials - concrete is strong in compression and steel is strong in tension. It is used widely in construction for buildings, bridges, tunnels and other structures due to its high strength and durability.
The document contains 55 multiple choice questions related to civil engineering topics like construction management, structures, materials, transportation, environmental engineering and geotechnical engineering. The questions are designed to test objective knowledge of definitions, principles, appropriate applications and industry standards.
Bar Bending Schedule (BBS) is a chart which gives a clear picture of bar length, diameter of bar ,bar mark ,location of bar.
It allow workers to place steel properly.
The document discusses building maintenance, common defects, and remedial methods for RCC structures. It describes three main common defects: foundations, walls, and concrete/RCC frames. For foundations, common issues include differential settlement, uplift of shrinkage soil, and dampness. For walls, issues include cracking, dampness penetration, and failure during cyclones. For concrete frames, common problems discussed are seepage/leakage, spalling of concrete, and corrosion of steel reinforcement. The document provides detailed remedial methods for addressing each of these defects.
The document discusses recommendations for improving the earthquake resistance of multistory reinforced concrete buildings based on deficiencies observed in past earthquakes. Key recommendations include:
1) Structural engineers and architects should be familiar with relevant seismic codes and consider soil conditions, foundation type, and structural system to avoid irregularities.
2) Soft first stories created by open ground floors or mid-height floors should be strengthened to avoid collapse due to stress concentration.
3) Floating columns and other discontinuities should be avoided to prevent large overturning forces.
4) Inertial forces from heavy rooftop tanks should be considered in design.
Seismic Analysis of Multi Storied Irregular Building using Flat Slab and Gri...IRJET Journal
This document analyzes the seismic performance of multi-story buildings with flat slab and grid slab structures in seismic zones III and V. Finite element software ETABS is used to model T-shaped and L-shaped buildings with 15 stories and both slab systems. Response spectrum analysis is conducted to determine parameters like base shear and storey shear. The results show that grid slab structures experience higher base shear values than equivalent flat slab buildings in both zones. In conclusion, grid slab structures perform poorer seismically compared to flat slab structures for the building geometries and conditions analyzed.
Seismic Drift Control in soft storied RCC buildingsIJERA Editor
The document discusses seismic drift in reinforced concrete (RC) buildings with soft first stories. It analyzes a 6-story RC building model in different seismic zones using STAAD-Pro software. Response spectrum analysis was performed and results like average displacement and inter-story drift are presented in tables for the bare frame and with a soft story at the ground floor. The analysis shows drift exceeds permissible limits for some zones, especially for the soft story model. Therefore special consideration is needed in design of buildings with vertical irregularities like soft stories.
Inelastic seismic response of single-story structure in hilly areas owing to ...IRJET Journal
This document summarizes a study that examines the inelastic seismic response of single-story reinforced concrete structures in hilly areas subjected to sloping ground and bidirectional ground motions. Three typical single-story structural models are developed with columns of varying heights due to slope angles of 15, 25, 35, and 45 degrees. The study analyzes the response of these structures both with and without beam-column joints. It also evaluates using a tuned liquid damper and masonry infill walls as mitigation techniques to reduce vibration and deformation from earthquakes. The conclusions of the study could help update seismic design code provisions for structures in hilly terrain.
Basic points on earthquake resistant building
- Design considerations and different techniques employed to resist building from collapse during earthquake
Seismic design codes in India outline procedures for designing earthquake-resistant structures. The Indian Standards provide criteria for seismic analysis and design of buildings according to their location within seismic zones. Key aspects covered include structural configuration, lateral strength, stiffness, ductility. IS 1893 specifies how to calculate seismic design forces based on zone factor, importance factor, response reduction factor, and average response acceleration coefficient. Structures must be designed to withstand minor, moderate, and major earthquakes without collapse through sufficient strength, stiffness, and ductility provided by code-compliant reinforcement detailing.
SEISMIC EVALUATION OF EXISTING RC BUILDING BY PRAVIN PISE.pptpravin45743
This document provides an overview of seismic evaluation and strengthening of existing reinforced concrete buildings according to Indian standard IS 15988:2013. It discusses the history of reinforced concrete construction in India. It also describes what a structural audit involves and defines seismic evaluation as an approved process to evaluate deficiencies that prevent a building from achieving life safety objectives. The document outlines the evaluation criteria, process, types of evaluations including preliminary and detailed, and describes steps involved in a preliminary evaluation.
This document is the Indian Standard Criteria for Earthquake Resistant Design of Structures, Part 1: General Provisions and Buildings (Fifth Revision). It summarizes the changes made in this fifth revision, including revising the seismic zone map to have four zones instead of five, changing the seismic zone factor values, specifying response spectra for different soil types, revising the formula for estimating building natural period, adopting response reduction factors, and revising other design provisions. The purpose is to incorporate latest research in earthquake-resistant design and experience from past earthquakes into the standard.
This document is the foreword for the Indian Standard Criteria for Earthquake Resistant Design of Structures Part 1: General Provisions and Buildings. It provides the following key details:
1) This standard provides guidelines for earthquake-resistant design of structures in India, where several regions experience strong earthquakes. Previous revisions in 1970, 1975, and 1984 updated the standard based on new seismic data and experience.
2) The current revision splits the standard into 5 parts covering different structure types. Part 1 contains general provisions and guidelines specific to buildings.
3) Major changes in the current revision include revising seismic zone maps and factors, specifying response spectra for different soil types, revising equations for building
This document discusses foundations and shallow foundations. It begins by explaining that foundations transfer loads from the superstructure to the soil and must not exceed the soil's bearing capacity. It then differentiates foundation design from other structural elements due to soil-structure interaction and other challenges. Finally, it describes several types of shallow foundations including isolated, combined, strap, strip, and raft foundations.
This document provides an overview of foundation design, including:
1) It defines the two major requirements of foundation design as sustaining applied loads without exceeding soil bearing capacity and maintaining uniform settlement within tolerable limits.
2) It differentiates between shallow and deep foundations, with shallow foundations including isolated, combined, strap, and strip footings and deep foundations including pile foundations.
3) It explains considerations for foundation design such as minimum depth, thickness, and determining bending moments and soil bearing capacity.
EFFECT OF SEISMIC LOAD ON REINFORCED CONCRETE MULTISTORY BUILDING FROM ECONOM...IAEME Publication
This paper aims at studying the effect of earthquake loading on the constructional
design of a 20-storey reinforced concrete residential building from economical point
of view. This type of loading should be taken into considerations now in Iraq
especially after the earthquake of 7.3 magnitude that occurred in November 2017 near
the city of Halabja by about 31 kilometers. The same reinforced concrete multistory
building was designed twice; once with traditional gravity dead and live loading and
the second with adding earthquake loading in order to discuss the difference from
structural and economical points of view. A commercial package ETABS2018 was
used to analyze this 60-meter-high building. The building was analyzed according to
the American code ASCE7-10, while it was designed according to ACI 318-14. A huge
increase in the steel reinforcement amounts in columns, beams, slabs and shear walls
were recorded due to taking the seismic load into considerations. More specifically,
the reinforcing steel amounts increased by about 327%, 165%, 40% and 91.3% for
columns, beams, slabs and shear walls, respectively. Therefore, cost was raised by
about 328%, 165%, 40% and 91.3% for columns, beams, slabs and shear walls,
respectively. It is worth to mention here that the maximum increase in main
reinforcement of beams was observed on the storey 10. Whereas, in slabs, the
maximum increase that was recorded in main steel reinforcement was happened from
the storey 8 to the building top. In columns, the main reinforcement increase was seen
on the 9th, 10th and 11th storeys. Finally, in shear walls, the main reinforcement
increase was seen in the 1
st
, 2
nd
and 3
rd
storey due to effect lateral shear forces
The document provides details about the Structural Design and Drawing course CE8703 taught at Vivekanandha College of Technology for Women. It includes the course objectives, units covered, outcomes, design and drawing exercises, textbooks and code books referenced. The key topics covered in the course are design and drawing of retaining walls, flat slabs, bridges, liquid storage structures, industrial structures, girders and connections. The course aims to provide students with knowledge of structural engineering design principles and skills to design and draw various reinforced concrete and steel structures.
Seismic Performance and Shear Wall Position Assessment of the Buildings Resti...IRJET Journal
This document analyzes the seismic performance of buildings resting on sloping ground with different shear wall configurations using ETABS software. A 6-storey building model is analyzed on slopes of 15, 20, and 25 degrees with 8 different shear wall layouts. Results show that maximum story displacement and base shear decrease while story drift ratio decreases as more shear walls are added. Placing shear walls on all sides is most effective at reducing seismic response. As slope increases, story displacement and base shear also increase. Shear walls are most effective at reducing displacement along the slope direction. Therefore, shear walls improve seismic performance of buildings on sloping sites, and placement is important to consider slope direction.
This document summarizes the analysis and capacity based earthquake resistant design of a multi-storey reinforced concrete building. It begins with an introduction describing the need for earthquake resistant design of multi-storey buildings. It then describes the experimental program and methodology for capacity based design. This includes designing beams to act as ductile weak links and columns to remain elastic. The document then provides details of analyzing a G+6 building model in STAAD Pro, including load calculations and modeling the 3D reinforced concrete frame. It concludes with sections on capacity based design basics and analyzing the frame for gravity and seismic loads.
This document is a seminar report on foundations and their types. It discusses shallow foundations like isolated, wall, combined, and strap footings as well as raft foundations. It also discusses deep foundations like pile foundations. Pile foundations transfer loads through skin friction and end bearing. Piles can be friction piles that transfer load through skin friction or end bearing piles that transfer load through end bearing. The report provides details on pile foundation classification and properties that affect foundation selection like soil bearing capacity, properties, and distribution of base pressure. It aims to study different foundation types and their uses based on soil and structural load conditions.
Seismic Performance of Flat Slab Structures Under Static and Dynamic LoadsIRJET Journal
This document presents research on analyzing the seismic performance of flat slab structures under static and dynamic loads. Models of flat slab structures with varying lateral stiffness were created, from flexible columns only to stiffer combinations of columns and shear walls. The models were subjected to seismic and dynamic loads, and the structural responses like natural periods, base shear, displacement, and inter-story drift were studied. The results showed that providing edge beams and shear walls strengthened flat slab structures seismically. Key aspects analyzed included the natural period, base shear, displacement, and inter-story drift of flat plate and flat slab structures with different configurations, under static and dynamic seismic loads.
IRJET- A Study on Seismic Analysis of RC Framed Structures on Varying Slo...IRJET Journal
This document presents a study on the seismic analysis of reinforced concrete framed structures located on varying slope angles, with and without shear walls. 12 models of a 10-story building were developed with slope angles of 0°, 11.25°, 22.5°, and 45° to analyze seismic performance. The models were analyzed using ETABS software for equivalent static and response spectrum analysis according to Indian seismic codes. Results for parameters like base shear, story shear, story displacement, and story drift were obtained and compared for models with shear walls at corners, corners and edges, and without shear walls. In general, models with shear walls performed better in reducing seismic demands.
Earthquake Resistance Design-Impact On Cost Of Reinforced Concrete BuilidingsIJMER
Earthquakes strike suddenly, violently and without warning at any time of the day or night.It
is highly impossible to prevent an earthquake from occuring, but the damage to the builiding can be
controlled through proper design and detailing. Hence it is mandatory to do the sesmic analysis and
design to structure against collapse. This study addresses the performance and variation of precentage
steel and concrete quantity of R.C framed structure in different seismic zones and influence on overall
cost of construction. This study mainly focuses on the comparision of percentage steel and concrete
quantities when the builiding is designed for gravity loads as per IS 456:2000 and when the builiding is
designed for earthquake forces in different seismic zones as per IS 1893:2002. A five storied R.C.C
framed structure has been analyse and designed using STAAD ProV8i. Ductile detailing has been done
in conformation with IS:13920
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1. 1
STEPS FOR SAFE DESIGN AND CONSTRUCTION OF
MULTISTOREY REINFORCED CONCRETE BUILDINGS
1. Introduction:
A large number of reinforced concrete multistoreyed frame buildings were heavily damaged and
many of them collapsed completely in Bhuj earthquake of 2001 in the towns of Kachchh District
(viz., Bhuj, Bhachao, Anjar, Gandhidham and Rapar) and other district towns including Surat and
Ahmedabad. In Ahmedabad alone situated at more than 250 kilometers away from the Epicentre of
the earthquake, 69 buildings collapsed killing about 700 persons. Earlier, in the earthquake at Kobe
(Japan 1995) large number of multistoreyed RC frame buildings of pre 1981 code based design were
severely damaged due to various deficiencies. Such behaviour is normally unexpected of RC frame
buildings in MSK Intensity VIII and VII areas as happened in Kachchh earthquake of January 26,
2001. The aim of this paper is to bring out the main contributing factors which lead to poor
performance during the earthquake and to make recommendations which should be taken into
account in designing the multistoreyed reinforced concrete buildings so as to achieve their adequate
safe behaviour under future earthquakes. The Indian Standard Code IS:1893 was suitably updated in
2002 so as to address the various design issues brought out in the earthquake behaviour of the RC
Buildings. The paper highlights the main provisions of this code.
2. Causes of the Collapse of RC Frame Buildings and Recommendations
2.1 Ignorance of the Architects and Structural Engineers about the Contents of the relevant
earthquake resistant Building Codes :
Recommendation:-
The following BIS Standards will be mainly required for the design of RCC Buildings.
Architect’s and Structural engineer’s design office should have the current copies of these
standards available in their offices and all their staff should fully familiarize with the contents of
these codes:-
1. IS: 456 -2000 “Code of Practice for Plain and Reinforced Concrete”
2. IS: 875 Part 1 “Unit weights of materials”.
3. IS: 875-1987Design loads ( other than earthquake ) for buildings and structures, Part2
Imposed Loads
4. IS: 875-1987Design loads ( other than earthquake ) for buildings and structures ,Part 3 Wind
Loads
5. IS: 1904-1987 “Code of Practice for Structural Safety of Buildings: Foundation”
6. IS: 1498-1970 Classification and identification of soils for general engineering purposes
(First Revision)
7. IS: 2131-1981 Method of Standard Penetration Test for soils (First Revision)
8. IS: 1905-1987, Code of Practice for Structural Safety of Buildings: Masonry
9. IS:1893(Part-I)-2002 "Criteria for Earthquake Resistant Design of Structures (Fifth
Revision)”.
10. IS:13920-1993, "Ductile Detailing of Reinforced Concrete Structures subjected to Seismic
Forces - Code of Practice"
11. IS: 4326-1993, "Earthquake Resistant Design and Construction of Buildings - Code of
Practice (Second Revision)"
12. IS-NBC-2005: National Building Code of India.
Note: The design offices should keep in touch with BIS-CE division to keep track of any amendments
issued or further revisions.
2. 2
2.2 Softness of Base Soil:
The soft soil on which most buildings in Ahmedabad were founded would have affected the
response of the buildings in three ways:
(i) Amplification of the ground motion at the base of the building;
(ii) Absence of foundation raft or piles;
(iii)Relative displacement between the individual column foundations vertically and laterally, in the
absence of either the foundation struts as per IS: 4326 or the plinth beams;
(iv)Resonance or, semi-resonance of the whole building with the long period ground waves;
(v) In the absence of the beam at plinth or, ground level, the length of ground storey columns gets
increased, which increases the flexibility of the ground storey and if the columns become ‘long’
the buckling moments due to P- Δ effect will increase bonding to cause collapse of the columns.
(vi) If the soil is sandy and water table is high, it may liquify. See IS:1893-2002 Cl 6.3.5.2 and
Table 1 for minimum N (corrected values) for safety and carryout soil liquefaction analysis by
standard procedures available in the literature. The adverse effects of liquefaction may be seen in
Figs. 1, 2 & 3.
Recommendation:-
Soil exploration at the buildings site must be carried out at sufficient points and to sufficient depth
so as to give the following data:
(i) Soil classification in various layers and the properties like grain size distribution, fields density,
angle of internal fritting and cohesion a plastic and liquid limits and coefficient of consolidation
of cohesive sites.
(ii) Position of water table just before and just after monsoon.
(iii)SPT values and CPT values.
(iv)The output results should include liquefaction potential, safe bearing capacity and the type of
foundation to be adopted, viz. (i) individual column footing of given width (ii) combined row
footing or (iii) raft foundation or (iv) Pile foundations.
(v) Chemical analysis of soil to find if it has any harmful elements to the concrete, if so, precautions
to be taken in making the foundations.
(vi)Chemical analysis of water to be used in making the Concrete mixtures.
2.3 Soft-first Storey:
Open ground storey (stilt floor) used in most severely damaged or, collapsed R.C. buildings,
introduced ‘severe irregularity of sudden change of stiffness’ between the ground storey and upper
storeys since they had infilled brick walls which increase the lateral stiffness of the frame by a factor
of three to four times. Such a building is called a building with ‘soft’ ground storey, in which the
dynamic ductility demand during the probable earthquake gets concentrated in the soft storey and
Fig. 1
The Building Sank evenly about 1 m
due to soil liquefaction. The displaced
soil caused a bulge in the road.
Fig. 3
The solid building tilted as a rigid
body and the raft foundation rises
above the ground
Fig. 2
This inclined building sank unevenly
and leans against a neighbouring
building
3. 3Providing R.C. Shear Wall
Providing Brick infills between
columns
Largest size stilt columns
Bracings in the columns of open ground storey
Fig. 7:- Remedial Measures for Soft Storey
the upper storeys tend to remain elastic. Hence whereas the ‘soft’ storey is severely strained causing
its total collapse, much smaller damages occurs in the upper storeys, if at all.
Behaviour of soft first storey buildings (buildings on stilts or with open plinth) during earthquakes
may be seen in Figs. 4, 5 & 6.
Recommendation:-
In view of the functional requirements of parking space under the buildings, more and more tall
buildings are being constructed with stilts. To safeguard the soft first storey from damage and
collapse, clause 7.10 of IS: 1893-2002 (Part 1) provides two alternative design approaches
(i) The dynamic analysis of the building is to be carried out which should include the strength and
stiffness effects of infills as well as the inelastic deformations under the design earthquake force
disregarding the Reduction Factor R.
(ii) The building is analysed as a bare frame neglecting the effect of infills and, the dynamic forces
so determined in columns and beams of the soft (stilt) storey are to be designed for 2.5 times the
Fig. 4
Sway mechanisms with soft
storey ground floors (Izmit,
Turkey 1999
Fig. 5
Soft first storey collapsed, upper
part of the building fall onto the
ground, (kachchh, 2001)
Fig. 6
Soft Storey (Open Plinth), Vertical
Split between two blocks (Bhuj)
4. 4
storey shears and moments: OR the shear walls are
introduced in the stilt storey in both directions of the
building which should be designed for 1.5 times the
calculated storey shear forces.
Some remedial measures to counter the bad performance are
shown in Fig. 7.
Some times a soft storey is created some where at mid-height
of the multi-storey building, for using the space as restaurant
or gathering purposes, see fig.8. Such soft storey in building
also collapsed in Kutch and Kobe earthquakes. For such a
case also, the storey columns should be designed for the
higher forces OR a few shear walls introduced to make up for
the reduced stiffness of the storey.
2.4 Bad Structural System:
The structural system adopted using floating columns, for
reasons of higher FSI is very undesirable in earthquake zones
of moderate to high intensity as in Zone III, IV & V since it
will induce large vertical earthquake forces even under
horizontal earthquake ground motions due to overturning
effects.
Recommendation:-
The structural engineer should provide for the load path in the
building from roof to the foundation. For example, a building
with floating columns requires transfer of the floating column
loads to horizontal cantilever beams through shear forces. The
load path, therefore, is not vertical but changes from vertical to
horizontal members before reaching the foundation. Sometimes
similar situations arise within the frames where, for any reason,
either the beam is missing or a column is missing. These are
structural discontinuities and should better be avoided as far as
possible. Other irregularities such as those defined in Table 4
& 5 of IS: 1893-2002 (Part 1) become the cause for large
torsional moments and stress concentration in the buildings
which should better be avoided by the architect and structural
engineer in the initial planning of the building configuration.
Otherwise, they should be carefully considered in structural
analysis and properly detailed in the structural design.
2.5 Heavy Water Tanks on the Roof:
Heavy water tanks add large lateral inertia forces on the
building frames due to the so called ‘whipping’ effect under
seismic vibrations, but remain unaccounted for in the design.
See the fall of such water tank in Fig.10
Recommendation:-
All projected systems above the roof top behave like secondary
elements subjected to roof level horizontal earthquake motions
which act as base motions to such projecting systems. To
Fig.10
5 storey R.C., collapse of open plinth, water
tank at top dislocated (Bhuj)
Fig.8:- Collapse of soft middle storey in a
building at Bhuj.
Fig.9:-Floating columns
Fc= Floating Columns
Cb= Cantilever Beams
Fc
Fc
Cb
Cb
5. 5
All the upper floors weak in long directions
(Izmit, Turkey 1999)
account for such heavy earthquake forces, IS:1893-2002 (Part 1) provides in clause 7.12 that their
support system should be designed for five times the design horizontal seismic co-efficient Ah
specified in clause 6.4.2. Similarly any horizontal projections as the balconies or the cantilevers
supporting floating columns, the cantilevers need to be designed for five times the design vertical
co-efficient as specified in clause 6.4.5 of IS: 1893-2002 (Part 1)
2.6 Lack of Earthquake Resistant Design:
Many buildings in Gujarat were not designed for the
earthquake forces specified in IS:1893, which was in existence
from 1962, revised in 1970, 1976 & 1984. The applicable
seismic zoning in Gujarat had remained the same as adopted in
1970 version. It is the same even in 2002 version of IS:1893
(Part I).
Inspite of that, the structural designers ignored the seismic
forces in design. It may also be stated that most buildings are
designed against lateral load in the transverse direction. Hence
they collapse in the longitudinal directions.
Proper arrangement of columns is shown in
Fig. 11 which would give adequate seismic
resistance along both axes of the building.
Recommendation:-
It does not need emphasizing that all
buildings including the multistoried
buildings should be designed in accordance
with IS: 1893 (Part 1) and IS: 4326 – 1993.
The salient features of the design will be
presented in Para 3.0 in this guide.
2.7 Improper Dimensioning of Beams &
Columns:
The structural dimensioning of beams and
columns was inadequate in terms of provisions
in IS: 13920-1993 and also for proper
installation of reinforcements in Beam-Column
joints as per IS: 456 and IS: 13920.
Recommendation:
The relative dimensions of beams &
columns become very important in tall
buildings from the point of view of
provision of longitudinal & transverse
reinforcement in the members as well
as the reinforcement passing through
and anchored in the beam-column
joints, permitting enough space for
proper concreting and without
involving any local kinking of the
reinforcing bars. The practice of using
small dimension columns like 200 or
WEAK
STRONG STRONG
STRONG
Fig.11:- Lateral Strength of Building Frame
Fig.13:- Plan of Reinforcement in Beams & Columns
6. 6
230 mm and beams of equal width is totally unacceptable from the reinforcement detailing view
point. Infact for permitting the beam bars passing through the columns, without any local bending
then straightening (introducing kinks), the proper scheme would be to use wider columns than the
beams. Minimum dimensions of beams and columns, also limiting aspect ratios of the two members,
are specified in IS: 13920 which need to be adhered to.
2.8 Improper Detailing of Reinforcement:
In detailing the stirrups in the columns, no conformity appeared to satisfy lateral shear requirements
in the concrete of the joint as required under IS 4326- 1976 and IS: 13920-1993. The shape and
spacing of stirrups seen in collapsed and severely damaged columns with buckled reinforcement was
indicative of non-conformity even with the basic R.C. Code IS: 456-1978.
Recommendation:
In respect of proper detailing of reinforcement in beams, columns, beam-column joints as well as
shear walls, all the provisions in IS:13920 have to be carefully understood and adopted in design.
The philosophy of over-design of beams in shear to force flexural hinge formation before shear
failure, confining of highly compressed concrete in columns and the use of properly shaped shear
stirrups with 135 degree hooks are some low-cost but extremely important provisions. For overall
safety of the frame, design based on the concept of strong-column, weak-beam system should be
adopted as far as practical. It may be mentioned that the full ductility details as specified in IS:
13920 permit the use of the High Reduction Factor R=5 which would make the design economical.
But if such ductility details are not adopted, the Reduction Factor is permitted as only 3.0, which
means that the design force will become 1.67 times the case when full ductile detailing is adopted
which may indeed turnout to be more expensive and at the same time brittle and relatively unsafe
(see fig.13).
Fig.13:- Detailing of reinforcement (Overlapping Hoops & Crosstie)
7. 7
2.9 Short Column Detailing
In some situations the column is surrounded by walls on
both sides such as upto the window sills and then in the
spandrel portion above the windows but it remains exposed
in the height of the windows. Such a column behaves as a
short column under lateal earthquake loading where the
shear stresses become much higher than normal length
columns and fail in shear. (See fig. 14)
Recommendation:
To safe guard against this brittle shear failure in such
columns the special confining stirrups should be provided
throughout the height of the column at short spacing as
required near the ends of the columns.
2.10 Torsional Failures
Torsional failures are seen to occur where the symmetry is
not planned in the location of the lateral structural elements
as for example providing the lift cores at one end of the
building or at one corner of the building or
unsymmetrically planned buildings in L shape
at the street corners. Large torsional shears are
caused in the building columns causing there
torsional shear failures (See fig.15).
Recommendation:
Where site requirements of from functional
requirements control the building plan shape,
either it should be split into two symmetrical
rectangular blocks by providing separation
sections of appropriate with between the
blocks or the structural elements should be so
adjusted that the centre of stiffness and the
centre of mass should coincide along both axis
of the building needless to say that any non-coincidence of the centre of mass and centre of stiffness
should be taken into design calculations as per IS:1893
2.11 Pounding Damage of Adjacent Buildings
Severe damage even leading to collapse are
seen due to severe impact between two
adjacent buildings under earthquake shaking if
the adjacent blocks of a building or two
adjacent buildings are of different heights with
floors at different levels and with inadequate
separation. Such buildings can vibrate out of
phase with each other due to very different
natural frequencies thus hitting each other
quite severely (see fig.16).
Recommendation:
Fig.15:- Very unsymmetrical building
Fig.16:- Pounding damage of adjacent buildings
Fig.14:- Damage
to buildings due to
short column
effect on columns
8. 8
Fig. 17:- Infill wall damage
To avoid such pounding damage the amount of separation between them should be liberally
provided so as to cater for the combined maximum out of phase displacements. A simple
recommendation is given in IS:4326 (Cl.5.1.2) for flexible as well as stiff buildings which must be
adopted as a minimum to avoid the possibility of pounding between two unsimilar buildings/blocks
2.12 Lack of Stability of Infill Walls
The infill walls were not properly attached either to
the column or the top beams for stability against
out-of-plane bending under horizontal earthquake
forces. Their cracking and falling was widespread
(See Fig. 17).
Recommendation:
Stability of infill walls is important in two ways:
first, they introduce their brittle failure due to the
diagonal compression in the panel and or diagonal
tension cracking; secondly, and more important is
their lateral stability under out of plane earthquake
force acting on their own mass. While conducting the retrofitting studies of three lifeline buildings
in Delhi, the 114 mm thick brick infill walls have turned out to be one of the main issues to handle
while retrofitting the building so as to save the inmates and the property inside from damage due to
the failure of the infill walls. It has been found that such walls will have to be contained with in pairs
of vertical angles spaced at 1.2 – 1.5 m apart. Therefore, while designing a new multistoried
building, the stabilisation of the infill wall panels should be properly considered either by providing
confining angles near the top or by providing slits on the vertical sides and stabilising by the means
of vertical angles or channels.
2.13 Poor Construction Quality:
The construction quality of the damaged R.C. buildings was found to be much below that desired, as
seen by the cover to reinforcement in the damaged members and the bad quality of concrete in the
columns in 150 to 300 mm length just below the floor beams and within the beam column joints.
Recommendation:
Needless to say that if the quality of construction is not commensurate with the quality of design,
even a well planned and a well designed building can show extremely bad behavior under
earthquake shaking. It should be remembered that during earthquake shaking all bad quality
constructions will be revealed and nothing can be kept hidden. Good quality of construction will
include: proper mixing and quantity of water, good quality sand and aggregates, designed quantity
of cement in the mix, proper mixing of all the ingredients with control on water cement ratio,
adequate compaction in the placement of concrete preferably by using vibrators, proper placement
of steel with control on the cover to steel and adequate curing before striking of the form work. The
engineer incharge of the construction should personally be present at site to supervise all operations.
He should have appropriate sampling and testing of materials carried out in a recognized laboratory,
the results of test being kept in well maintained register for inspection by quality audit team. He
should organize the taking of sample of steel reinforcement & concrete cubes in adequate numbers
which should be tested at the specified age of testing.
3. Some Important Codal Design Provisions:
In the last few years the author has had the opportunity of reviewing many reinforced concrete
building designs prepared by well-established consulting companies as well as individual
9. 9
consultants and felt the need of preparing brief guidelines so that no important Codal provisions are
missed out and the various design details for achieving better construction in the field and better
ductile performance in the event of a great earthquake are ensured. Thus a safe and ductile building
could be achieved.
3.1 Building Configuration
For achieving basic structural safety of buildings under postulated earthquake forces the first
important requirement is that the building should be designed with symmetrical configuration both
horizontally and vertically. In any case the seismic force resisting elements must be planned
symmetrically about the centre of the mass of the building. IS:1893 (Part 1-2002) presents in detail
in cl.7.1 the various types of irregularities which should be avoided as far as possible or corrected by
planning the structural resisting elements. The present day requirements of large column free spaces
inside can be met by designing strong frames on the periphery of the building so as to resist most of
the horizontal design seismic forces and relieving the internal columns relatively from the
earthquake forces. For this purpose shear walls may be provided in the building perimeter to
increase the stiffness in both principal axes of the building as compared with the internal columns
which could be designed basically for vertical loads.
3.2 Calculation of Loads
The loads will include the following:
(i) Dead Loads: These will include the weight of all components at each level, viz., roof
including water tanks, Barsatis, Parapets, roof finishes, slabs, beams, elevator machine room
etc. and including all plasters and surface cladding etc., and each floor level including fixed
masonry or other partitions, infill walls, columns, slabs and beams, weight of stairs,
cantilever balconies, parapets and plastering or cladding wherever used. The unit weights
may be taken from IS:875 (Part 1) or ascertained from the manufacturer.
(ii) Imposed Floor Loads: IS 875 (Part 2) deals with the imposed loads on roofs, floors, stairs,
balconies, etc., for various occupancies. There is a provision for reduction in the imposed
loads for certain situations, e.g. for large span beams and number of storeys above the
columns of a storey. The earthquake code IS: 1893 (Part 1)-2002 permits general reduction
in roof and floor imposed load when considering the load combination with the earthquake
loading. But the two types of reductions, that is, in IS: 875 (Part 2) and IS: 1893 (Part 1) are
not to be taken together.
3.3 The Earthquake Load:
For working out the earthquake loading on a building frame, the dead load and imposed load and
weights are to be lumped at each column top on the basis of contributory areas. The imposed load is
to be reduced as specified in IS: 1893 (Part1)-2002 for seismic load determination. Let us call them
Wi at ith floor and Wn at the nth level at the roof level for a n-storey building. Hence the total load
at the base of the building just above the foundation will be
n
W = Σ i=1 W i + Wo
where Wo is the weight of elements in the ground storey.
3.4 Earthquake Resistant Design
Now the following steps may be taken:
(a) Estimate fundamental time period Ta using empirical expressions given in the Code IS: 1893-
10. 10
2002.
Ta = 0.075 H0.75
, IS: 1893 Cl.7.6.1 for bare frame along each axis
Tax = 0.09h/√d along x-axis IS: 1893 Cl.7.6.2 for frame with substantial infills
Ta z = 0.09h/√b, along z-axis, IS: 1893 Cl.7.6.2 for frame with substantial infills
where h is the height of the building and d and b are the base dimensions of the building
along x and z axis respectively.
(b) Calculate the design horizontal Seismic coefficient Ah
Now compute the fundamental time periods T/
x and T/
z for the bare frame along the two axes by
dynamic analysis. These are generally found to be higher than Tax and Taz respectively.
The design horizontal coefficient Ah is given by
Ah = (Z/2). (I/R). (Sa/g)
Take Z for the applicable seismic zone (IS: 1893 Cl.6.4.2),
Take I for the use importance of the building (IS: 1893 Table 2),
Take R for the lateral load resisting system adopted (IS: 1893 Table 7),
and take Sa/g for the computed time period values T/
x, Tax, T/
z and Taz with 5% damping
coefficient using the response spectra curves IS: 1893 Fig 2 for the soil type observed. Thus four
values of Ah will be determined as follows:-
In x-direction A/
hx for T/
x & Ahax for Tax
In z-direction A/
hz for T/
z & Ahaz for Taz
(c) Calculate the total horizontal shear (the base shear)
The design value of base shear VB
VB = Ah W
as per 1893 Cl.7.5.3.
For design of the building and portions thereof, the base shear corresponding to higher of Ahax
and A/
hx, similarly between Ahaz and A/
hz will be taken as minimum design lateral force.
(d) Seismic Moments and Forces in Frame Elements:
Calculate the seismic moments and axial forces in the columns, shears and moments in the
beams by using the seismic weights on the floors/(column beam joints) through an appropriate
computer software (having facility for using floors as rigid diaphragm and torsional effects as
per IS: 1893:2002).
It may be performed by Response Spectrum or Time History analysis. The important point is
that according to IS: 1893 Cl.7.8.2., the base shear computed in either of the dynamic method,
say V/
B shall not be less than VB calculated under Cl.7.5.3 using Ahax and Ahaz. If so, then all
shears, moments, axial forces etc worked out under dynamic analysis will be increased
proportionately, that is, in the ratio of VB/V/
B.
(e) Soft Ground Storey
It must be designed according to Cl.7.10 of IS: 1893-2002.
11. 11
4. Method of Design
Structural design of various members has to be done by Limit State Method, as per IS 456-2000 for
which the following load combinations should be used to work out the maximum member forces:-
Using
DL for DEAD LOAD
LL for LIVE LOAD
EQX for SEISMIC LOAD (X) DIRECTION
EQZ for SEISMIC LOAD (Z) DIRECTION
The load combinations for analysis and design will be taken as follows:
1. (DL+LL)*1.5
2. (DL+LL+EQX)*1.2
3. (DL+LL+EQZ)*1.2
4. (DL+LL-EQX)*1.2
5. (DL+LL-EQZ)*1.2
6. (DL+EQX)*1.5
7. (DL+EQZ)*1.5
8. (DL-EQX)*1.5
9. (DL-EQZ)*1.5
10. 0.9DL+EQX*1.5
11. 0.9DL+EQZ*1.5
12. 0.9DL-EQX *1.5
13. 0.9DL-EQZ*1.5
The members (beams, columns, shear walls etc.) and their joints will be designed for the worst
combination of loads, shears and moments.
MATERIALS:
a) Cement: Ordinary portland cement conforming to IS 269 - 1976 shall be used along with fly ash
after carrying out the design mix from approved consultant.
b) Reinforcement: Cold twisted high yield strength deformed bars grade Fe 415 conforming to IS:
1786-1985, or preferably TMT bars of standard manufacturer e.g. TATA Steel, SAIL or equivalent
shall be used.
The following grades of concrete mix may be adopted or as required for safe design:
(a) For RCC columns in lowest few storeys : M35
(b) For RCC columns in the middle few storeys : M30
(c) For RCC columns in the top few storeys : M25
(d) For beams, slabs, staircase etc. : M20
(e) For raft foundation : M 20 or 25
(f) Max. Water cement Ratio : 0.45
(g) Minimum cement content : 300 kg/m3
of concrete.
(h) Admixtures of approved brand may be used as per mix design
CLEAR COVER TO ALL REINFORCEMENT:
For mild Exposure and fire rating of 1 hr. following clear covers may be adopted
(a) For foundation R.C.C.:
i) Footings : 60 mm.
12. 12
ii) Raft : 60 mm.
(b) For columns : 40 mm
(c) For Beams : 25 mm or main bar dia. whichever is more.
(d) For Slab : 20 mm.
4.1 Ductile Detailing
After designing the frame column-beam, shear walls and foundation by limit state theory as per
IS: 456:2000, all details of longitudinal steel, overlaps, shear capacities, confining reinforcement
requirements, stirrups and ties etc. shall be worked out using the provisions of IS: 13920-1993.
The drawings should clearly show all the adopted details.
5. Concluding Remarks
In a nut-shell, the seismic safety of a multi-storeyed reinforced concrete building will depend upon the
initial architectural and structural configuration of the total building, the quality of the Structural
analysis, design and reinforcement detailing of the building frame to achieve stability of elements and
their ductile performance under severe seismic lading. Proper quality of construction and stability of
the infill walls and partitions are additional safety requirements of the structure as a whole. Any
weakness left in the structure, whether in design or in construction will be fully revealed during the
postulated maximum considered earthquake for the seismic zone in the earthquake code IS: 1893.
Acknowledgement:
The figures have been taken from various sources to suit the text message and are anonymously
acknowledged.
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