study of behavior of precast beam column joints

8/12/2019 Study of behavior of precast beam column joints..

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Chapter 1 INTRODUCTION

1.1. Precast System

The concept of pre-cast construction include those buildings, where the majority of structural

components are standardized and produced in a plants in locations 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.

The main features of this type of construction are as follow:

The division and specialization of the human workforce.

The use of tools, machinery and other equipment, usually automated, in the

production of standard, interchangeable parts and products.

ompared to site cast concrete, pre-cast concrete is easy to erect and less affected by

adverse weather conditions.

!lant casting allows increased efficiency, high quality control and greater control on

finishes.

This type of construction requires a restructuring of entire conventional construction process

to enable interaction between design phase and production planning in order to improve and

speed up construction.

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1.2. Types of Precast Systems

"epending upon the load bearing structures, pre-cast systems can be divided into the

following categories-

a# $arge-panel systems

b# %rame systems

c# &lab-column systems with walls

d# 'i(ed systems

1.2.1. Large panel systems: This type of systems appointed for the multi-story

structures composed of large walls and concrete slab panels connected in vertical

and horizontal directions so that the wall panels enclosed the appropriate spaces

for the rooms within a building. These panels form a bo( like structure. )othhorizontal and vertical panels resist gravity loads. *all panels are usually one

story high. +orizontal floors and roof panels span either as one-way or two-way

slabs. *hen properly joined together this horizontal members act as a diaphragm

and transfer the lateral loads to the wall."epending upon wall lay-out there are

three basic configurations of large panel building-

ross wall systems: - The main walls that resist gravity and lateral loads

are placed in the short direction of the building.

$ongitudinal wall systems: - The walls resisting gravity and lateral loads

are placed in the longitudinal direction usually there is only one

longitudinal wall.

Two-way systems: - The walls are placed in both directions. Thickness of

wall panels ranges form /mm for interior walls to 0//mm for e(terior

walls. %loor panel thickness is 1/mm. wall panel length is equal to the

room length, typically on the order of .2m to 0.1m.

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1.2.2. !rame Systems: - !recast frames can be constructed using either linear

elements or spatial beam column sub-assemblages. !recast 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 withforming, 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. +owever, rigid beam-column connections

are used in some cases, when the continuity of longitudinal reinforcement

through the beam-column joint needs to be ensured.

1.2.". Sla#Col$mn systems %&th shear %alls: These systems rely on shear walls

to sustain lateral load effects, whereas the slab-column structure resists mainlygravity loads. There are two main systems in this category:

$ift-slab system with walls: 3n the $ift-slab system, the load-bearing

structure consists of precast reinforced concrete columns and slabs.

!recast columns are usually two stories high. 4ll precast structural

elements are assembled by means of special joints. 5einforced concrete

slabs are poured on the ground in forms, one on top of the other. !recast

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.

!re-stressed &lab-olumn &ystem: - The pre-stressed slab-column system

uses horizontal prestressing in two orthogonal directions to achieve

continuity. The precast concrete column elements are to 0 stories high.

The reinforced concrete floor slabs fit the clear span between columns.

4fter erecting the slabs and columns of a story, the columns and floor

slabs are prestressed by means of prestressing tendons that pass throughducts in the columns at the floor level and along the gaps left between

adjacent slabs. 4fter prestressing, the gaps between the slabs are filled

with in situ concrete and the tendons then become bonded with the spans.

&eismic loads are resisted mainly by the shear walls 6precast or cast-in-

place# positioned between the columns at appropriate locations.

1.". Precast Concrete Str$ct$ral 'lements

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4 precast building is constructed by assembling and connecting various prefabricated

elements required in the building structure.

1.".1. Precast Sla#s: !recast slabs are cast in a factory environment and include

the following pre-stressed concrete options-

+ollow core units

"ouble-tee units

&olid concrete units

)eam and block floors

)ia(ial voided slabs

Figure 1.1: - Double-tee slab panel

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Figure 1.2: - Hollow core Slab

1.".2. Precast (eams: )eams are used for suspended flooring. )eams are typically

used as ledges for other forms of precast flooring to sit on, but can also be used

as a flooring option in their own right. They are generally manufactured to suit

each particular situation and profiles can include Tee-beams, $-beams,

5ectangular beams, etc. )eams can be either reinforced or prestressed.

Figure 1.3: - Precast Beams of various cross-sections

1.".". Precast col$mns: !recast concrete columns are modular in design in order

to be made into different heights. *idths are 7, 87 and 97. olumns are not

structural, but can be used as such only after a structural engineering has adapted

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them to a building. +alf columns can also be used against a building which can

add variety to the architectural design. !recast columns can be produced as

either single storey core-bell columns or multi storey core-bell columns. &ize

and length of column can be design to suit to the architect design requirement.

olumns can either be rectangular or circular in section.!rojecting rebar can beprovided for tying in to in-situ floors. ptions for foundation connections

include cast in base plates, dowel tubes or projections.)eam support is achieved

by flared head, corbels or bolt-on brackets.

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Figure 1.: - Precast columns wit! corbel !ea"s

1.".). Precast *alls: 4 wall system can be comprise of flat or curved panels,

window or mullion panels, ribbed panels, or a double tee. ;ach type of panel

will readily accommodate openings for doors and windows. 3n the interest of

both economy and functions, precast panels should be as large as possible, while

considering production efficiency and transportation and erection limitations. )y

making panels as large as possible, numerous economies are realized, the

number of panels needed is reduced, fewer joints, lower erection cost and fewer

connections are required. !anels may be design for used in either horizontal or

vertical positions.

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Figure 1.#: - Precast $all Panels

1.".+. Shear %all: 3n many structures, it is economical to take advantage of

inherent strength and in-plane rigidity of e(terior wall panels by designing them

to serve as the part of the lateral load resisting systems. *alls taking horizontalloads form the effect of wind or earthquake are referred to as shear walls. &hear

walls are used as the most common and economical lateral force resisting system

and have been utilize widely in buildings up to 0/ stories. &hear wall system

effectiveness is dependent largely upon panel to panel connection design. 4

significant advantage of jointed construction is in the inherent ease of defining

load paths through connections. 4s such, it is relatively easy to separate a precast

concrete lateral force resisting system performance from that of the vertical load

bearing frame. &hear walls are vertical members, which transfer lateral forces, in

or parallel to the plane of the wall, from superstructure to foundation. Thus,

shear walls act as vertical cantilever beams. &hear walls are placed at appropriate

locations within and around the building perimeter according to the architectural

and functional design requirements.

1.".,. Precast foot&ngs: !recast footings are recent innovations.


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are environmental friendly.

are the best material choice for residential and light commercial

foundations.

Figure 1.%: - Precast &solate" Footings

There are many other precast components like piles stairs etc. which have their

own need in precast system design.

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Chapter 2 LIT'R-TUR' SUR'/

(oo0s an Stanars

!recast concrete structures by =3'.&.;$$3T presents a hapter 8: >oint ?

onnection and hapter @: )eam and olumn connection which give connection

design e(amples and different connection details.

(eam an Col$mn Connect&ons:The design and construction of connections and joints is the most important

consideration in precast concrete structures. Their purpose is to transmit forces between

structural members andAor to provide stability and robustness. There may be several

different ways of achieving a satisfactory connection, e.g. bolting, welding, or grouting,

but whichever is used the method should be simple and must convey unambiguous

messages to the site operatives. The joints should not be designed to resist applied

serviceability and ultimate loads, which are relatively straightforward to predict and

calculate. )ut they should be adequate in case of abnormal loads due to fire, impact,

e(plosions, subsidence, etc. %ailure of the joints should not, under any circumstances,

lead to structural instability. 3t is therefore unfortunate to have to report that information

on the design of joints for abnormal loading conditions in precast concrete structures is

scarce-provisions to guard against this are only provided in form of continuous column

and floor ties, which in many cases bypass the joints.

*ithin a single connection there may be several load transmitting joints, and so it is

necessary to distinguish between a joint and a connection. 4 joint is the action of forces

6e.g. tension, shear, compression# that takes places at the interface between two 6or

more# structural elements in many instances there may be an intermediate medium, such

as rubber, steel, felt, cementitious mortar, epo(y mortar, etc. The design of the joints

will be greatly influenced by how much these materials differ from concrete.

The definition of a connection is the action of forces 6e.g. tension, shear, compression#andAor moments 6bending, torsion# through an assembly comprising one 6or more#

interfaces. The design of the connection is therefore a function of both the structural

elements and of the joints between them. 3n addition to the actions of forces, connection

design must consider the hazards of fire, accidental damage, effects of temporary

construction and inaccurate workmanship, and durability.

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Types of (eamCol$mn Connect&ons:

There are various types of connections are used in precast concrete system. &ome of

basic connections are listed here-

a) Classifcation on basis o design and construction terms in

vertical or horizontal continuity directions-

Type : - the vertical member is continuous 6both in design and construction terms#

and horizontal elements are connected to it:

+idden connection, for which there is an enormous range, some of which are

shown in figure.

Bisible connection, such as shallow and deep corbels or nibs, shown in figure.

Type : - the vertical member is discontinuous 6only in construction terms# and the

horizontal elements are either structurally continuous or separate across the

junction:

The ends of beams are simply supported and dowelled at the column head.

ontinuous beams are supported and dowelled at the column head. 4 beam-

beam half joint is made some distance from the face of the column, or else thebeam forms a balcony cantilever.

b) Classifcation on basis o construction method adopted on

site-

"ry joints: - "ry joints are constructed by bolting or welding together steel

plates or other steel inserts cast into the ends of the precast panels for this

purpose. The force transfer in structures with dry joints is accomplished at

discrete points.

*et joints: - *et joints are constructed with cast-in situ place concrete poured

between the precast panels. To ensure structural continuity, protruding

reinforcing bars from the panels 6dowels# are welded, looped, or otherwise

connected in the joint region before the concrete is placed. *et joints more

closely appro(imate cast-in-place construction.

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Figure 2.1: - '(pes of beam-column connections

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c) Classification on basis of type of action for which it is designed to resist-

&hear joints: -&hear transfer is required at joints between precast wall elements

and between floor elements. 4t longitudinal joints between hollow core units

shear transfer is required horizontally as well as vertically. onnections

between precast beam elements or floor elements and a cast in situ topping

may require shear resistance to obtain an adequate behaviour in the final state.

Tension joints: -The ability to transfer tensile forces is normally secured by

means of various types of tie bars, anchor bars and other connecting devices of

steel. Tensile capacity is often required between wall elements used for

stabilization, between floor elements and between precast floors and their

supports. "epending on the position of the ties these connections can be more

or less capable of transferring bending moments, even if this was not intended

by the design. Cnintended tensile resistance can sometimes appear in

connections, for instance due to bond between the short end face of a floorelement and the joint concrete in the support joint nearby.

ompression joints: -Transfer of compressive forces is an important function ofconnections at horizontal joints in precast walls, in connections between precast

column elements, and at support connections of precast beams.

%le(ure joints: -%le(ural resistance is required for instance when a precast column isfi(ed at the base, or when continuity is needed at interior supports of beams or floors.

4lso for beam ? column connections in moment resisting frames, fle(ural resistance

may be required.

Torsion joints: - Torsional capacity is needed at support connections of simplysupported beams that are loaded eccentrically with respect to the sectional shear

centre. This may for instance be the case for one-sided ledge beams used for precast

floors.

The various type of beam-column connections are shown below-

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Figure 2.2: - Beam-to-column face connections. )s(mmetricall( loa"e" beams re*uire couple

connections to prevent beam twisting

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Figure 2.3: - Beam-to-column !ea" connections. ) bearing pa" + groute" "owels are also

present.

Figure 2.: - Beam-to-column connection wit! t!e use of corbel !ea"

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4ll connections must have adequate strength, stiffness and ductility. The requirements

for the mechanical behaviour of different types of connections depend on their

intended purpose, and may differ widely whilst being perfectly suited to their need.

%or all three t(pes of connections we will plot t!e curve of ,oa" P v/s Deformation

0 as-

Figure #.1: - Sc!ematic representation of be!aviour of "ifferent t(pes of connections

3n connection 4, a large elastic stiffness may be required for cyclic loading, whilst the

ductility is not important because there is no danger of overload in connector. 3n ),

non-linear deformation may be satisfactory if the connection is concerned only with

strength. 3n , low stiffness with post-yield ductility may be required if e(cessive

deformations are acceptable.

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4ll connections must have a mechanical tensile force capacity, even compression and

especially shear connections. ontact bond and friction is not allowed. 4ll members

must therefore have embedded anchors. ;ven if tension is not present in the structure

model, tensile capacity is provided for the purposes of robustness under abnormal

conditions.

Figure #.2: - elations!ip between structural be!aviour of connections wit! respect

to t!e member to w!ic! it is attac!e"

onnection D is a suitable connection because its deformation capacity is greater than

that required by the connected member 6dashed line, known as the beam line# the

residual strength, rather than the actual ultimate strength, is often used in design. )ut

E is not a satisfactory connection because failure takes place in a brittle manner prior

to matching the requirements of the member.

"uctile capacity, F!AFy is achieved by increasing the strength of brittle parts of

connections. )rittle parts of the connections are well known such as dowels in shear,

short bolts in tension, welds, congested reinforcement zones and confined rebaranchor lengths.

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!3 "esign +andbook 1- The precast concrete institute 6!3# +and book gives design

dimensions, capacity of different type of precast elements which is based on a design

guideline according to 43 08 code.

)ook by &yaiful chapter: The fle(ure and shear design of corbel bracket give full

understanding of corbel design with appropriate diagram and design e(amples. The all

design aspects are shown in design of corbel.

>5 &cientific and !olicy report: "esign Guidelines for onnections of !recast

&tructures under &eismic 4ctions, hapter 0: )eam to olumn connection give

connections with "owels

The principal failure modes for longitudinal action are listed hereunder: - breaking of the dowel connection due to combined shear, tension and fle(ure

on steel bar and bearing

stresses on concrete

spalling of the concrete edge of the beam due to tensile stresses

spalling of the concrete edge of the column due to tensile stresses.

The principal failure modes for transverse action are listed hereunder:

fle(ural failure of the bearing section due to the action of

pull-out of the tensioned dowel under the action due to &liding shear failure under the action of .

;(perimental and 4nalytical study: - Bidjeapriya and >aya presented the e(perimental

investigation of one third scale precast concrete column connections subjected to

reverse cyclic loading. The !recast specimen and monolithic specimen were designed

for the same strength. %or the precast connection, the beam was connected to the

column with corbel using a cleat angle with a single stiffener and for the precast

connection, cleat angle with two stiffeners were used. Testing system as shown in %ig.

..The sub-assemblage specimens were subjected to cyclic displacement controlled

lateral loading, applied at the end of beam. The ultimate load carrying capacity, load

ratio, hysteretic behaviour, energy dissipation, equivalent viscous damping ratio,

ductility factor and strength degradation of both the precast and monolithic specimen

were measured and their performance was compared. The results showed that ultimate

load carrying capacity of the monolithic specimen was superior to both the precast

specimens. The precast specimens were found to e(hibit satisfactory behaviour when

compared to the monolithic specimen in terms of energy dissipation and ductility.

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!revious years '.Tech paper for e(perimental setup and theory H/'$,

/'$I, '$/IJ.

Figure 2.#: - ,oa"ing assembl( use" to test beam-column 4unction

Chapter " ('- -ND COLUN CONN'CTIONS IN PR'C-ST S/ST'

".1. Des&gn of Connect&on for 34" storey hostel #$&l&ng

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%or applying concept of connection design in precast system, 0-storey hostel building

is selected which was designed in cast in-situ manner by 6/Kbcl )atch#. %or study

purpose, the beam column junction at ground storey for column has been selected.

4ll designed loads and moments are taken as per the calculation of thesis. The

proposed plan and elevation of the hostel building is shown in figure 0. below.

The specification of junction and reactions developed at the junction are as follows-

"etails:

'aterial used-

Grade of concrete: 'I

Grade of steel: %e9I

"etails of elements to be connected-

olumn dimensions 6#: 60//L0//# mm

)eam dimensions 6)0I#: 60//L0I/# mm

"esigned forces and moments on the connection

&hear force: 08 =oshi, .B.5. 'urty and '.!. >aisingh, Zyclic )ehaviour of !recast 5

onnections7, ournal.

'ehta 4nand, Z4nalytical and ;(perimental &tudy on &teel %iber 5einforced oncrete

orbel7, aya, Z!erformance of ;(terior !recast )eam-olumn "owel

onnection under yclic $oading7. 4nna Cniversity, hennai-1///I, 3ndia.

5. Bidjepriya ? =.!. >aya, Z;(perimental 3nvestigation of !recast oncrete )eam-

olumn *et onnection under yclic $oading7, 4nna university, hennai-1///I, 3ndia.

&agar ". &hah, 'ansi >ain, 5ujuta 'ehta, Z4nalysis and "esign of !recast )uilding

&ystem7,


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study of behavior of precast beam column joints

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