precast building structures and it's seismic performance

M-TECH. SEMINAR REPORT

PRECAST BUILDING STRUCTURES AND IT’S SEISMIC PERFORMANCE Submitted by AJAY V JOSEPH REG. NO: 202181

Under the guidance of Mr. MANISH JOSE Asst. Professor, Department of Civil Engineering

DEPARTMENT OF CIVIL ENGINEERING ST.JOSEPH’S COLLEGE OF ENGINEERING & TECHNOLOGY, PALAI CHOONDACHERRY P.O, BHARANANGANAM. 2014-2016

ST. JOSEPH’S COLLEGE OF ENGINEERING AND TECHNOLOGY, PALAI (Approved by AICTE and affiliated to Mahatma Gandhi University) An ISO 9001: 2008 Certified College

CERTIFICATE This is to certify that the seminar report entitled “PRECAST BUILDING STRUCTURES AND IT’S SEISMIC PERFORMANCE” submitted by “AJAY V JOSEPH”, Register No: 202181 to the Department of Civil Engineering, St. Joseph’s College of Engineering & Technology, Palai, in partial fulfillment of the requirements for the degree of Master of Technology in Civil Engineering from Mahatma Gandhi University, Kottayam, Kerala, is an authentic report of the seminar presented by him.

Prof. B. V. Mathew

Mrs. Tilba Thomas

Mr. Manish Jose

Head of the Department

Seminar Coordinator

Seminar Guide

ACKNOWLEDGEMENT First and the foremost, I shall thank God Almighty who gave me the inner strength, resource and ability to complete the work successfully, without which all my efforts would have been in vain. I express my sincere gratitude to our chairman, Msgr. Philip Njaralakkatt and our project director, Dr. P. J. George for giving me the opportunity to do the seminar. I am grateful to our principal, Dr. C. J. Joseph for providing me good facilities and proper environment for developing my seminar and to do it in the required way. I am thankful to Prof. B. V. Mathew, Head of Department of Civil Engineering, for his valuable advice and motivation. I wholeheartedly thank my seminar guide Mr. Manish Jose (Asst. Professor, Dept. of Civil Engineering) for his valuable advice and support. Also I express my heartfelt thanks to our seminar coordinator Mrs. Tilba Thomas (Asst. Professor, Dept. of Civil Engineering), for her helpful feedback and timely assistance. I convey my sincere thanks to all other faculties for their help and encouragement. I thank all my friends who have helped me during the work, with their inspiration and cooperation. I truly admire my parents for their constant encouragement and enduring support, which was inevitable for the success of this venture. Once again I convey my gratitude to all those persons who had directly or indirectly influenced on the work.

Ajay V Joseph

i

ABSTRACT Precast concrete systems represent an efficient alternative for building construction. Some countries considered the use of precast concrete in earthquake resisting structures with suspicion because of their bad performance in major earthquakes. The primary cause for this damage was not any inherent deficiency in precast concrete elements, but was due to the use of poor connection details between precast elements and not ensuring deformation compatibility between the earthquake force resisting system and gravity frames in the structures that contribute to sustaining the gravity loads. Introduction of a new ductile moment resisting precast connection suitable for RC frames located in high seismic zones. The proposed system enables easy construction work by minimizing cast-in-place concrete volume and eliminating the need for formworks, welding, bolting and pre stressing. Also seismic performance of precast buildings can be improved by using dissipating devices like friction damper. This paper is mainly looking for types of precast systems, precast structural elements, typical connections, use of energy dissipative devices, case studies of precast structures etc. Key words: Precast concrete, Moment resisting connections, codal provisions, prototype damper

ii

TABLE OF CONTENTS Section No.

Title

Page No.

ACKNOWLEDGEMENT………………………………………………...…………

i

ABSTRACT …………….…………………………………………………………….

ii

LIST OF FIGURES……………………………………………...…………………..

v

LIST OF ABBREVIATIONS / SYMBOLS…………………………..…………

viii

CHAPTER 1

INTRODUCTION

1.1

GENERAL

1

1.2

FEATURES OF PRECAST CONCRETE

1

1.3

PAST PERFORMANCE OF PRECAST STRUCTURES WITH STRUCTURAL WALLS

4

1.4

LIMITATIONS OF PRECAST CONCRETE APPLICATION IN SEISMIC REGIONS

6

CHAPTER 2

LITERATURE REVIEW

CHAPTER 3

TYPES OF PRECAST SYSTEMS

3.1

LARGE PANEL SYSTEM

10

3.2

FRAME SYSTEMS

11

3.3

SLAB-COLUMN SYSTEMS WITH SHEAR WALLS

12

3.3.1

Lift slab system with walls

12

3.3.2

Pre- stressed Slab Column system

13

CHAPTER 4 4.1

PRECAST STRUCTURAL ELEMENTS

PRECAST CONCRETE FLOOR SYSTEMS iii

15

TABLE OF CONTENTS(Contd…)

Section No.

Title

Page No.

4.1.1

Flat Slab Floors

15

4.1.2

Hollow Core Concrete Slab Floor

16

4.1.3

Double Tee Floor

16

CHAPTER 5 ELEMENTS

TYPICAL CONNECTIONS OF PRECAST CONCRETE

CHAPTER 6 NEW DUCTILE MOMENT RESISTING CONNECTION FOR PRECAST CONCRETE FRAME IN SEISMIC REGIONS

CHAPTER 7 CODAL PROVISIONS RELATED TO THE SEISMIC PERFORMANCE OF PRECAST CONCRETE SYSTEMS

CHAPTER 8 IMPROVING SEISMIC PERFORMANCE OF PRECAST BUILDINGS USING DISSIPATIVE DEVICES

CHAPTER 9

CONCLUSIONS

REFERENCES

32

DISCUSSIONS

34

iv

LIST OF FIGURES Figure

Title

Page No.

1.1

Collapse of precast school building

2

1.2

Poor column details in Kocaelli earthquake

2

1.3

Failure of beam column pin connection at top of poorly

3

detailed column in Northridge earthquake 1.4

Shear failure at base of precast concrete in Kocaelli

3

earthquake 1.5

Collapse of the second level of the Northridge Fashion

5

Center parking garage 1.6

1.7

Precast concrete structure that sustained no structural damage when subjected to Kobe earthquake in Japan Precast concrete building that sustained no damage when

5

6

subjected to the 1999 Kocaelli earthquake in Turkey 3.1

Large panel concrete building under construction

8

3.2

Frame system

9

3.3

Lift slab building

10

4.1

Precast slab

11

4.2

Precast girders

11

4.3

Precast columns

11

4.4

Precast walls

12

4.5

Precast concrete stairs

12

4.6

Cross section of a precast flat slab floor

13

v

LIST OF FIGURES(Contd…) Figure

Title

Page No.

4.7

Cross section of hollow-core concrete slab floor

13

4.8

Cross section of a double tee floor

14

5.1

Column to column connection

15

5.2

Slab to beam connection

16

5.3

Beam to column connection

16

6.1

Detailing of reinforcement in the connection zone of the

18

precast Elements 6.2

Detailing of interior and exterior pre cast connections

19

7.1

Damage of seat due to movement of floors

20

7.2

Failure of floors due to inability of topping to transfer

21

shear stress 7.3

Required bearing length at the support of a member in

21

relation to its clear span 8.1

Friction device applied to beam to column connections of

22

precast frames 8.2

Cross section of friction device

23

8.3

Top displacement of the structures analyzed for different

24

seismic intensity levels: Multistory frame and one-story industrial Building 8.4

Maximum demand-to-capacity ratio for different columns of the precast frame: ag=0.15g and ag=0.6g

vi

24

LIST OF FIGURES(Contd…) Figure 8.5

Title

Maximum demand-to-capacity ratio for different columns

Page No. 25

of the one story industrial building: ag=0.15g and ag =0.6g 8.6

Base shear of the structures analyzed for different seismic

26

Intensity levels: Multistory frame and one-story industrial building 8.7

Energy dissipated by structural elements of the structures analyzed for Seismic intensity levels: multistory frame and one-story industrial building

vii

27

LIST OF ABBREVIATIONS / SYMBOLS

Fy - Characteristic compressive strength of steel MEP - Mechanical Electrical Plumbing ag - Seismic intensity level

viii

Precast Building Structures and it’s Seismic Performance

CHAPTER 1

INTRODUCTION 1.1

GENERAL

The concept of precast (also known as “prefabricated”) construction includes those buildings, where the majority of structural components are standardized and produced in plants in a location away from the building, and then transported to the site for assembly. These components are manufactured by industrial methods based on mass production in order to build a large number of buildings in a short time at low cost.

1.2

FEATURES OF PRECAST CONCRETE

1. The division and specialization of the human workforce 2. The use of tools, machinery, and other equipment, usually automated, in the production of standard, interchangeable parts and products 3. Compared to site-cast concrete, precast concrete erection is faster and less affected by adverse weather conditions. 4. Plant casting allows increased efficiency, high quality control and greater control on finishes 5. Precast helps to reduce site labour and form work 6. Precast concrete is ecological 7. Precast concrete is durable 8. Precast concrete is affordable 9. Precast concrete is versatile Due to the lack of understanding of the basic nature of seismic behaviour, the precast concrete structures were viewed with skepticism in seismic regions. Some countries considered the use of precast concrete in earthquake resisting structures with suspicion because of their bad performance in major earthquakes. Examples of poor behaviour of precast concrete building structures during 1976 Tangshan (China), 1985 Michoacan (Mexico), 1988 Armenian, 1994 Northridge and 1999 Kocalli earthquakes due to improper design and detailing of ductile element, inadequate diaphragm action, poor joint and connection details. 1|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Damage to precast school buildings at Gujarat in 2001Bhuj earthquake is another example of failure due to the poor connections between structural elements is shown in fig.1.1. It is reported that roof planks resting on the beam shifted due to inadequate bearing area and lack of positive anchorage. A monolithic behaviour of frames, and diaphragms action of floors could not be achieved due to poor connections.

Fig. 1.1: Collapse of precast school building (Ghosh et.al, 2006)

Fig. 1.2: Poor column details in Kocalli earthquake (Ghosh et.al, 2006) 2|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 1.3: Failure of beam column pin connection at top of poorly detailed column in Northridge earthquake (Ghosh et.al, 2006)

Fig. 1.4: Shear failure at base of precast concrete in Kocalli earthquake (Ghosh et.al, 2006) 3|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


1.3

PAST PERFORMANCE OF PRECAST STRUCTURES WITH STRUCTURAL WALLS

Significant structural damage to concrete frame buildings and precast structures has been observed in moderate to large earthquakes that have occurred from 1960 to1999. Fintel (1991), who examined the structural damage of buildings after several of these earthquakes, reported based on earthquake damage observed until the late1980s that there was not a single concrete building with structural walls that experienced any significant damage. Thomas and Sritharan (2004) conducted a detailed literature review on the seismic performance of precast structures with structural walls during the seismic events that occurred between 1960 and 1990. The most damaging recent earthquakes, which alerted the engineering community to closely examine the seismic behavior of precast structures, were the 1994 Northridge earthquake in California, the 1995 Kobe earthquake in Japan, and the 1999 Kocalli earthquake in Turkey. In the 1994 Northridge earthquake, several precast concrete parking structures performed poorly, causing significant structural damage (see Figure 2.1). The primary cause for this damage was not any inherent deficiency in precast concrete elements, but was due to the use of poor connection details between precast elements and not ensuring deformation compatibility between the earthquake force resisting system and gravity frames in the structures that contribute to sustaining the gravity loads. A postearthquake investigation of the structural damage following the Northridge earthquake revealed that the lateral load resisting precast shear walls remained uncracked, while precast concrete elements of the floor system collapsed A positive aspect of all the devastation caused by the 1995 Kobe earthquake was good performance of several precast and prestressed concrete structures. Apartment buildings in Japan are typically two-to-five stories in height, and some of these buildings also include precast concrete walls as the primary elements to resist both the gravity and lateral loads. None of these buildings that included the precast walls experienced any damage in the Kobe earthquake while cracking of concrete members was observed in cast-in-place concrete buildings. In the 1999 Kocaeli earthquake, a

4|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 1.5: Collapse of the second level of the Northridge Fashion Center parking garage (Ghosh et.al, 2006) few apartment buildings with large precast wall panels connected in vertical and horizontal directions were found to have performed more than adequately amidst significant devastation.

Fig. 1.6: Precast concrete structure that sustained no structural damage when subjected to Kobe earthquake in Japan (Ghoshet.al, 2006)



Fig. 1.7: Precast concrete building that sustained no damage when subjected to the 1999 Kocaeli earthquake in Turkey (Ghosh et.al, 2006)

1.4 LIMITATIONS OF PRECAST CONCRETE APPLICATION IN SEISMIC REGIONS There are several limitations that restrict the use of precast concrete in seismic regions. The primary limitation stems from poor performance of precast concrete frame buildings in the past seismic events. Although the poor performance of buildings was largely attributed to the use of substandard materials, poor construction practices, and insufficient design of connections, it had contributed to the decline of designer’s confidence in the use of precast concrete in seismic design. Extensive damage and catastrophic failure of precast RC structures in major earth quake was mainly due to failure of joints and inadequate ductility, which highlighted the ductile connection in precast structures.



CHAPTER 2

LITERATURE REVIEW Bindurani.P et al in December 2013 studied an efficient alternative for building construction. The behaviour of a precast system depends on connections and it should be modelled properly in the computational models for analysis and design. This study presented the modelling of connections in a wall type precast building system. A case study on a 23-storeyed building, made up of precast wall panels and slabs, to study the modelling of vertical joints in terms of shear transfer, is presented in the paper. Two computational models were investigated to find the effect of modelling the vertical joints between the wall panels, on the drifts and the generated forces in the walls. It was observed that the model, which was not considering any shear transfer through the vertical joints, tend to provide conservative results in terms of amount of steel requirement. The emulative monolithic wall system seems to be adequate in moderate seismic zones. The provisions of tie reinforcements, reinforced shear keys and dowel bars provide the required structural integrity for the precast system to avoid progressive collapse.

Fabio Biondini et al in February 2011, studied about the structural members of precast one-storey or low-rise multi-storey concrete frames for industrial or commercial buildings are often directly exposed to the environment without any protection. The aim of this paper is to investigate the seismic performance of this type of structure considering the material degradation induced by the diffusive attack of aggressive agents, like sulphate and chloride, that may lead to deterioration of concrete and corrosion of reinforcement. The time-variant structural performance of the critical cross-sections of the columns, where plastic hinges are expected to occur during a seismic event, is investigated in terms of bending moment versus curvature relationships. Push-over and push-pull cyclic analyses are then carried out over the structural lifetime to assess the global structural performance in terms of base shear forces and displacement ductility. In this way, even though the lifetime evolution of the dynamic behaviour under ground motion is not captured, it can be shown how the hierarchy of member strengths, and hence the energy-dissipating failure mode 7|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


claimed for a capacity design of the structure, can be affected by the time-evolution of damage. The proposed procedure is applied to investigate the lifetime seismic performance of one-storey and three-storey frame structures. The results show a significant reduction of both base shear strength and displacement ductility over the structural lifetime and highlight the importance of a lifetime approach to seismic assessment and design of concrete structures. Recent research investigations demonstrated that precast structures, under condition of a proper capacity design of connections, can achieve the same seismic performance of cast-in-place structures in terms of global strength and ductility.

S.K. Ghosh et al in November 2006, inferred that precast concrete structures could be built in areas of high seismicity, such as California, only under an enabling provision of the ACI 318 Building Code Requirements for Structural Concrete, which is adopted by all model codes used in the country. The provision allows precast concrete construction in a highly seismic area “if it is demonstrated by experimental evidence and analysis that the proposed system will have a strength and toughness equal to or exceeding those provided by a comparable monolithic reinforced concrete structure”. The enforcement of this vague, qualitative requirement was, for obvious reasons, nonuniform. The need for specific enforceable design requirements for precast structures in regions of high seismicity was apparent for quite some time.

J. Witzany, T. Cejka & R. Zigler in October 2010, presented the results of an experimental and theoretical analysis of the response of a prefabricated wall structure of a multi-story building to technical seismicity effects. The experimental investigation employed a model of a seven-story carrying prefabricated wall structure of a prefabricated panel building in the scale of 1:3. The model of the prefabricated structure was gradually exposed to eight loading states, includ-ing the cyclic and monotonously rising loading. The cyclic load induced by Tira-vib electrodynamic exciter simulated technical seismicity effects. The drop of stiffness of the prefabricated system was monitored in the first place by measuring relative displacements between the wall units and the deformation of the whole system in horizontal, as well as vertical direction. Based on the analysis of the experimental 8|Page Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


results of the response of a prefabricated experimental system to a dynamic load, a relatively high level of the reliabil-ity and resistance of similar load-bearing prefabricated wall systems of multi-story buildings to the effects of standard technical seismicity with the frequency spectrum of seismic response and the magnitude of the seismic load within the verified scope may be reported.

Stefano Pampanin in June 2010, studied major advances have been observed in the last decade in seismic engineering with further refinements of performance-based seismic design philosophies and definition of corresponding compliance criteria. Following the worldwide recognized expectation and ideal aim to provide a modern society with high seismic performance structures, able to sustain a design level earthquake with limited or negligible damage, emerging solutions have been developed for high-performance, still cost-effective, seismic resisting systems, based on adequate combination of traditional materials and available technology. In this paper, an overview of recent developments and on-going research on precast concrete buildings with jointed ductile connections, is given. These recently developed highseismic resisting systems, able to undergo inelastic deformation during a major seismic event with minor structural damage and re-centering capability, represent a major achievement in seismic engineering in the last decade and could be possibly considered a fundamental milestone in the historical development in the field. Similarly, the development started in the early 1990s of ductile connections able to accommodate high inelastic demand without suffering extensive material damage appears to be a promising and critical step forward for the next generation of highperformance seismic resisting systems based on the use of conventional material and techniques.



CHAPTER 3

TYPES OF PRECAST SYSYEMS Depending on the load-bearing structure, precast systems can be divided into the following categories:

3.1

i.

Large-panel systems

ii.

Frame systems

iii.

Slab-column systems with walls

iv.

Mixed systems

LARGE PANEL SYSTEMS

The designation “large-panel system” refers to multistory structures composed of large wall and floor concrete panels connected in the vertical and horizontal directions so that the wall panels enclose appropriate spaces for the rooms within a building. These panels form a box-like structure. Both vertical and horizontal panels resist gravity load. Wall panels are usually one story high. Horizontal floor and roof panels span either as one-way or two-way slabs. When properly joined together, these horizontal elements act as diaphragms that transfer the lateral loads to the walls. Depending on the wall layout, there are three basic configurations of large-panel buildings:

1) Cross-wall system: The main walls that resist gravity and lateral loads are placed in the short direction of the building.

2) Longitudinal-wall system: The walls resisting gravity and lateral loads are placed in the longitudinal direction; usually, there is only one longitudinal wall, except for the system with two longitudinal walls developed in Kazakhstan.

3) Two-way system: The walls are placed in both directions

10 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 3.1: Large panel concrete building under construction (Randy Simmons2003)

3.2

FRAME SYSTEMS

Precast frames can be constructed using either linear elements or spatial beamcolumn sub-assemblages. Precast beam-column sub-assemblages have the advantage that the connecting faces between the sub-assemblages can be placed away from the critical frame regions; however, linear elements are generally preferred because of the difficulties associated with forming, handling, and erecting spatial elements. The use of linear elements generally means placing the connecting faces at the beam-column junctions. The beams can be seated on corbels at the columns, for ease of construction and to aid the shear transfer from the beam to the column. The beam-column joints accomplished in this way are hinged. However, rigid beam-column connections are used in some cases, when the continuity of longitudinal reinforcement through the beam-column joint needs to be ensured. The components of a precast reinforced concrete frame are shown in Figure.



Fig. 3.2: Frame system (Randy Simmons 2003)

3.3 SLAB- COLUMN SYSTEMS WITH SHEAR WALLS These systems rely on shear walls to sustain lateral load effects, whereas the slabcolumn structure resists mainly gravity loads. There are two main systems in this category: i.

Lift-slab system with walls

ii.

Pre stressed slab-column system

3.3.1 Lift slab system with walls In the Lift –slab system, the load-bearing structure consists of precast reinforced concrete columns and slabs. Precast columns are usually two stories high. All precast structural elements are assembled by means of special joints. Reinforced concrete slabs are poured on the ground in forms, one on top of the other. Precast concrete floor slabs are lifted from the ground up to the final height by lifting cranes. The slab panels are lifted to the top of the column and then moved downwards to the final



position. Temporary supports are used to keep the slabs in the position until the connection with the columns has been achieved.

Fig. 3.3: Lift slab building (Randy Simmons 2003) 3.3.2 Pre stressed slab-column system The pre stressed slab-column system uses horizontal pre stressing in two orthogonal directions to achieve continuity. The precast concrete column elements are 1 to 3 stories high. The reinforced concrete floor slabs fit the clear span between columns. After erecting the slabs and columns of a story, the columns and floor slabs are prestressed by means of prestressing tendons that pass through ducts in the columns at the floor level and along the gaps left between adjacent slabs. After prestressing, the gaps between the slabs are filled with in situ concrete and the tendons then become bonded with the spans. Seismic loads are resisted mainly by the shear walls (precast or cast-in-place) positioned between the columns at appropriate locations.



CHAPTER 4

PRECAST STRUCTURAL ELEMENTS Precast concrete building structures include beams, column, frame, slab panel, folded plate or shell stairs and wall panels. These structures can be very well designed as gravity load and seismic load resisting system.

Fig. 4.1: Precast slab (Randy Simmons 2003)

Fig. 4.2: Precast girders (Randy Simmons 2003)

Fig. 4.3: Precast columns (Randy Simmons 2003) 14 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 4.4: Precast walls (Randy Simmons 2003)

Fig. 4.5: Precast concrete stairs (Randy Simmons 2003)

4.1

PRECAST CONCRETE FLOOR SYSTEMS

A few common types of pre-cast concrete floors used in New Zealand are discussed: (i) flat slab floor (ii) hollow-core concrete slab floor and (iii) double-tee floor.

4.1.1 Flat slab floors Flat slab floors can provide economic solutions up to 6 m span. It consists generally of a series of 75 mm thick precast, pre stressed concrete slabs with a reinforced concrete topping. The slabs are usually 1.2 m or 2.4 m wide, and require 75 mm end seating. 15 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 4.6: Cross section of a precast flat slab floor (Khare et.al, 2011) 4.1.2 Hollow-core concrete slab floor Fig. 4.1.2 shows a section of a precast, prestressed concrete hollow-core floor panel with continuous longitudinal voids to reduce self-weight. These floor slabs can span up to 18 m (at 400 mm depth) and provide a working platform immediately after being positioned. Hollow-core slabs are generally un-propped during the casting of the topping. Concrete topping on precast floors can be of about 65mm to 75mm.

Fig. 4.7: Cross section of hollow-core concrete slab floor (Khare et.al, 2011) 4.1.3 Double-tee floor. Another type of precast floor used for long spans is a double tee unit consisting of two prestressed ribs with an integral floor connecting top slab (Fig.4.8). The ribs can vary in depth from 200 to 600 mm, and the units are generally 2.4 m wide, although units may vary in size depending on the manufacturers. Double Tees typically span up to 19 m, and provide a safe platform, directly after placing, for subsequent work. 16 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 4.8: Cross section of a double tee floor (Khare et.al, 2011)



CHAPTER 5

TYPICAL CONNECTIONS OF PRECAST CONCRETE ELEMENTS Precast concrete members have various advantages in service and quality. In comparison with cast-inplace concrete. However the joints between prefabricated members have some issues. Joints can be considered as the weakest and most critical parts of a precast concrete structure. Precast concrete frame connection is not used extensively in high seismic regions of most countries. Connections in particular beam to column connection are the vital part of precast concrete construction. To satisfy the structural requirements of the overall frame each connection must have the ability to transfer vertical shear, transverse horizontal shear, axial tension and compression and occasionally bending moment and torsion between one precast component and another. The transfer of forces between components is eventually the behaviour of frames is governed by characteristics of the connections. However in practice the behaviour of precast connections is not well established and not fully understood to fulfill the requirements needed in the design and construction development of precast technology. The various structural element connections are shown in Fig. 5.1.

Fig. 5.1: Column to column connection (Robert et.al, 2003) 18 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 5.2: Slab to beam connection (Robert et.al, 2003)

Fig.5.3: Beam to column connection (Robert et.al, 2003) 19 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


CHAPTER 6

NEW DUCTILE MOMENT RESISTING CONNECTION FOR PRECAST CONCRETE FRAME IN SEISMIC REGIONS Moment-resisting beam–column connections are, in general, suitable systems to maintain lateral stability and structural integrity of the multi-storey precast concrete structures in high seismic zones. Experiment showed that the specimens detailed for seismic loads have adequate strength, ductility, and energy dissipation for ductile moment-resisting frames. The result of experimental study indicated that the precast connections can provide adequate strength and energy dissipation with respect to monolithic concrete specimens. Fig. 6.1 illustrates details of the developed interior and exterior moment-resisting connections for precast concrete frames. In the proposed system, prefabricated concrete columns are cast continuously in the elevation with a free space in the connection zone to connect beam elements. Four diagonal bars are used in the empty zone of the precast columns (i.e. beam–column joint core) to provide adequate strength and stability during the installation process. The diagonal bars behave like truss elements and can considerably increase the axial strength of the columns under construction/transportation loads. The shear links used in the connection core can prevent the buckling of the longitudinal and diagonal bars under the self-weight of the precast columns. In the connection zone, the precast concrete beams have a hollow U shape cross section. A longitudinal bar is used in the precast concrete U section to support diagonal stirrup bars, which can also provide adequate tensile strength to resist installation loads. The surface of precast members at the U section zone was smooth, and no slippage was observed between the precast members and the grout during the experimental tests. The length of the connection zone (i.e. plastic hinge zone) of the precast beams was calculated to be 600 mm. 20 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


After fixing the longitudinal reinforcement bars, the connection zone is filled with cast-in-place concrete to provide a good structural integrity between beam, column and slab elements. The bottom longitudinal reinforcement bars are spliced in the castin place area of the beam. The top reinforcement bars are continuous through the beam–column joint (as shown in Fig.6.2) and are fixed to the precast beams outside the connection zone with a layer of grout. Diagonal stirrup bars and U-shaped anchorages are used to provide enough shear strength before using cast-in-place concrete. The connection region is then grouted to form a moment-resisting beam– column connection. No diagonal bracing bar is used in the joint core of the monolithic specimens. The proposed precast connection can be easily assembled as it eliminates the need for welding or using mechanical splices for beam longitudinal reinforcement at joints. Temporary supports for beams are provided by means of steel angles on each side of the columns. The steel angles provide enough bearing area for sitting the RC beams and transferring the construction loads before in situ concrete becomes structural. Therefore, in the proposed system, there is no need for using formwork and temporary vertical supports for beam and slab elements. This can lead to a low-cost fast-construction system for multi-storey buildings, where multiple stories can be constructed at once.

Fig. 6.1: Detailing of reinforcement in the connection zone of the precast Elements (Parastesh et.al, 2014) 21 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 6.2: Detailing of interior and exterior pre cast connections (Parastesh et.al, 2014)



CHAPTER 7

CODAL PROVISIONS RELATED TO THE SEISMIC PERFORMANCE OF PRECAST CONCRETE SYSTEMS The provisions of American, New Zealand and Euro codes and guidelines related to the seismic performance of precast concrete systems are discussed in this section. These provisions have demonstrated that how the seismic performance of precast systems can be improved. This study will help in framing the codal provisions and guidelines in Indian perspective. Failure of precast concrete buildings in 1964 Alaska, 1976 Tangshan, China, 1988 Armenia, 1994 Northridge, 2001 Bhuj and 2008 Wenchan china earthquakes was mainly due to collapse of floors for some or other reasons. One of the main reasons of collapse of floors were loss of seat due to failure of support system, poor connections, excessive deformation of support system (beam elongation) and deformation incompatibility between the support and floor. Typical detail of the damage of seat of a floor resting on wall or beam support due to the movement is shown in Fig.7.1.

Fig. 7.1: Damage of seat due to movement of floors (Khare et.al, 2011) After this damage takes place, floors without topping fall due to their own weight. Earthquake vertical accelerations add on to this action. Floors with topping are also failed during these earthquakes when the top reinforcement could not transfer the shear force from the precast flooring to the supporting beam as shown in Fig. 7.2. 23 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 7.2: Failure of floors due to inability of topping to transfer shear stress (Khare et.al, 2011) A possible solution to avoid these failures can be by providing the sufficient seating incorporating the effect of all possible movements into account. Fig.7.3 shows such detail of required bearing length at the support suggested by NZS 3101: 2006.

Fig. 7.3: Required bearing length at the support of a member in relation to its clear span (Khare et.al, 2011)



CHAPTER 8

IMPPROVING SEISMIC PERFORMANCE OF PRECAST BUILDINGS USING DISSIPATIVE DEVICES A new type of friction damper for improving the seismic performance of precast concrete frame structures was introduced. The friction damper is used externally at selected beam-to column joints of the frame to dissipate energy during severe earthquakes. Fig 8.1 shows a prototype damper installed at the beam-to-column joint of an industrial precast frame. Each damper consists of five cast-steel components with four friction interfaces sandwiched in-between. Two of the damper components are connected to the beam, while the remaining three components are connected to the column. The friction interfaces are pre stressed. Under earthquake loading, relative rotations at the beam-to-column interface result in slip displacements at the friction surfaces between the beam and column damper components, thus dissipating energy. The device system is connected to the column and to the beam through simple bolted connections.

Fig. 8.1: Friction device applied to beam to column connections of precast frames (Marco Valente, 2013) 25 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


Fig. 8.2: Cross section of friction device (Marco Valente, 2013) Fig 8.3 presents the maximum top displacements registered for the structures under study for different seismic intensity levels (

ranges from 0.15g to 0.6g). A

considerable reduction of the maximum top displacements was observed in case of structures equipped with dissipating devices. The difference between the maximum top displacements of the structures resulted small for low-intensity level earthquakes, but it significantly increased in case of severe seismic actions. The numerical analyses showed that the effectiveness of the dissipative devices increased with the increase of the peak ground acceleration. It can be noted that the curves have a steeper slope for the unprotected structures, meaning an increased sensitivity to increases of the intensity level of the seismic action. The displacements were remarkably smaller in case of unprotected structures, because of the dissipative capacity given by the friction devices. In case of low-intensity level seismic actions the retrofitting intervention increased the stiffness of the building, without exploiting much the dissipative capacity provided by the friction devices.



Fig. 8.3: Top displacement of the structures analyzed for different seismic intensity levels: Multistory frame and one-story industrial Building (Marco Valente, 2013)

Fig. 8.4: Maximum demand-to-capacity ratio for different columns of the precastframe: ag=0.15g and ag=0.6g(Marco Valente 2013)



Fig. 8.5: Maximum demand-to-capacity ratio for different columns of the one story industrial building: ag=0.15g and ag =0.6g.(Marco Valente 2013) Fig 8.4 and Fig 8.5 show the values of the ratio between the maximum rotation obtained by numerical analyses and the ultimate rotation (demand-to-capacity ratio) for some reference columns of the two structures under study. Capacity and demand were computed in terms of chord rotation according to Eurocode 8. The results of the nonlinear dynamic analyses performed for different seismic intensity levels were reported to evaluate the effectiveness of the dissipative devices in function of the peak ground acceleration. The demand resulted to be smaller than the capacity (the ratio was always smaller than unity) for the reference seismic intensity level also in case of unprotected structures. The maximum values of the demand-to-capacity ratio in terms of chord rotation were observed for the internal columns, as subjected to high axial load. The application of the friction devices decreased the rotation demand at the 28 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


column base of the structures. In case of severe seismic actions the rotation reduction was significant producing a considerable decrease of the demand-to-capacity ratio. Moreover the numerical analyses showed that in structures equipped with dissipative devices the plastic demand concentrating at the column base developed for higherintensity level earthquakes with respect to unprotected structures, indicating a delay in the formation of the plastic hinges in case of protected buildings. The introduction of the friction devices decreased the damage at the column base, providing a considerable contribution to energy dissipation and to reduction of the top displacement. The results of the numerical investigations showed an increase of both strength and stiffness for the protected structures. The friction devices caused a moderate increase of the base shear for the investigated structures, as presented in Fig 8.6. The increment of the base shear was influenced by the values adopted for the slip force of the friction devices.

Fig. 8.6: Base shear of the structures analyzed for different seismic Intensity levels: Multistory frame and one-story industrial building (Marco Valente, 2013) The energy dissipated by the structural elements of the reference structures was significantly reduced by the insertion of the friction devices, as showed in Fig.8.7. The energy dissipation mostly concentrated in the device, decreasing the plastic demand in the structural elements of the reference structures. The energy dissipated by the protected structures, practically entirely due to the friction devices, showed a



considerable decrease with respect to the original structures, consistent with the significant reduction of the top displacements.

Fig. 8.7: Energy dissipated by structural elements of the structures analyzed for Seismic intensity levels: multistory frame and one-story industrial building (Marco Valente, 2013)



CHAPTER 9

CONCLUSIONS Precast concrete inherently provides versatility, efficiency, and resiliency resulting in improved quality, performance, and sustainability.Failure of precast concrete buildings during past earthquakes has raised a question mark in the construction of precast concrete buildings in seismic areas. A review of seismic performance and behavior of precast concrete structures indicates that the buildings constructed and designed incorporating seismic design concepts performed remarkably well. A brief review of codal provisions on the design and construction of precast concrete systems in American, New Zealand and Euro codes and practices is presented. A new ductile moment resisting precast connection suitable for RC frames located in high seismic zones. The proposed system enables easy construction work by minimizing cast-inplace concrete volume and eliminating the need for formworks, welding, bolting and pre stressing. Also seismic performance of precast buildings can be improved by using dissipating devices like friction damper. A significant reduction of top displacements was observed and the formation of the plastic hinges at the column base was delayed with respect to the unsupported structures. A moderate increase of the base shear was observed for the buildings protected by friction devices.



REFERENCES 1. Bindurani.P, A. Meher Prasad,and Amlan K. Sengupta . “Analysis of Precast Multistoreyed building – a case study”, International Journal of Innovative Research in Science, Engineering and Technology, Volume 2, Special Issue 1, December 2013. 2. Fabio Biondini, Alessandro Palermo and Giandomenico Toniolo, “Seismic Performance of concrete structures exposed to corrosion: case studies of low-rise precast buildings”,Journal of Structure and Infrastructure Engineering, Vol. 7, January–February 2011. 3. Ghosh S. K, Nakaki, Suzanne Dow and Krishnan Kosal . “Precast Structures in Region of High Seismicity”, International Journal of Civil, Architectural, Structural, Urban Science and Engineering,Vol.6,November 2006.

4. J. Witzany, T.Cejka and R. Zigler. “Prefabricated Multi-story structure exposed to Engineering Seismicity”,Journals of Challenges, Opportunities and Solutions in Structural Engineering and Construction ,October.2010. 5. Khare R. K., M. M. Maniyar, Uma S. R. and Bidwai V.B . “Seismic Performance and Design of Precast Concrete Building Structures: An Overview”, Journal of structural engineering, Vol.3 ,December 2011 . 6. Nuno Filipe Barata Feliciano, “Seismic Design of Precast Concrete Industrial Buildings”, Journal of Department of Civil Engineering of Instituto Superior Técnico, August 2011. 7. Stefano pampanin, “Emerging solution for high seismic performance of precast/ prestressed concrete building”,Journal of Advanced Concrete Technology,Vol.3 , June 2010. 8. ISN14213 (1994) “Code of Practice for construction of walls”. 32 | P a g e Semester II, M-Tech, Dept. of Civil Engg., SJCET Palai


9. IS 15916 (2011) “Building design and erection using prefabricated concrete – code of practice”. 10. EN 1992 1-1(2004) “Eurocode and design of concrete Structures”.



DISCUSSIONS i. What do you mean by demand capacity ratio? Demand capacity ratio is the ratio between the maximum rotation obtained by numerical analyses and the ultimate rotation for some reference columns of the two structures under study. ii. How does the load transfer occur in moment resisting connection until the cast in-situ concrete becomes structural? The U shaped cross section precast beam rests on a bearing plate. Until the cast in-situ concrete becomes structural the bearing plate helps to transfer the beam load to the columns and thereby to the foundations. iii. Where there any precast buildings that are damaged during the Kathmandu Earthquake? The buildings that were damaged or collapsed in Kathmandu earthquake were nonengineered buildings. That is those buildings that are made of mud mortar or buildings without any bands. No precast structure was found to be collapsed.
