Saudconsult Presentation 2013

7/27/2019 Saudconsult Presentation 2013

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Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM

Bridges Saudi Arabia 2013


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1. General Overview.

2. Problems Associated with Expansion Joints.

3. Connection Types Between Precast Pre-stressed

Bridge Girders Made Continuous Over Piers.

4. Showcasing the Design of Continuous Decks Over

Simple Spans Precast Pre-stressed Bridge Girders.

5. Conclusions.

6. References.


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1. General Overview


On the other hand, the aforementioned expansion joints cause maintenance problems and consequent

the durability of this type of bridges may be significantly improved by eliminating or reducing expansio

joints in their decks. Therefore, this type of superstructure may be designed as a series of simple spans b

their connections should be detailed for converting them to act as continuous spans for loads applied aft

continuity is established.


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1. General Overview (Contd.)


However, achieving continuity in bridge decks built

using precast pre-stressed girders induces secondary

stresses (shrinkage, creep, thermal stresses, etc.)

that can cause structural damage of the decks, unless

their analysis, design and construction have beenperformed properly.

Therefore, this transformation of simple-span precast

pre-stressed bridge girders to continuous spans, in

view of the difficulty in assessing the long-term

effects of time-dependent material behavior (aging,

creep, and shrinkage), makes its design a challengingtask for ensuring the constructibility, safety,

serviceability, and durability.


5/46 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOM

1. General Overview (Contd.)


Figure 1: Partial Continuity Detail Through

Continuous Separated Slab

Additionally, the detailed description and analysis

results of Staged Construction (including timedependent material behavior effects) Finite Element

Modeling of a case study of four-span simply

supported precast pre-stressed bridge girders made

continuous using continuous slab over piers, as

shown in Figure 1 (partial continuity)2)

and its

proposed typical continuity connection details are

presented and discussed.


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9/46 Modeling, Analysis and Design of Buildings AIT - Thailand ACECOMBridges Saudi Arabia 2013

Figure 3: Full Continuity Detail Method 2, Narrow In-situ Integra

Crosshead [BA 57/01]2)

Method 2: As shown in Figure 3, this method utilizes in-

situ integral crosshead which may be designed to develop

full continuity moments. The temporary supports are notrequired, permanent bearings may be in single or twin line

and the continuity reinforcement is provided in the slab

and at the bottom of bridge girders.

3.1 Full Continuity Methods (Contd.)

Figure 4: Full Continuity Detail Method 3, Integral Crosshead Castin Two Stages [BA 57/01]2)

Method 3: As shown in Figure 4, this method utilizes in-

situ integral crosshead which may be designed to develop

full continuity moments. The girders are supported on

stage 1 crosshead during erection. The crosshead is

monolithic with pier and the continuity reinforcement is

provided in the slab and at the bottom of girders.

The above methods 2 and 3 are the most commonly used methods for achieving full continuity. Method 2

has been extensively used in North America [BA 57/01]2).



AASHTO LRFD 20071) outlined design provisions for full continuity approach of bridges composed

simple span precast girders made continuous and states that this approach has been used successfully

several parts of the country. However, there are arguments about the effectiveness of this approach in casof composite bridge decks using precast pre-stressed girders. Partial continuity is generally preferred

full continuity in such structures because of the difficulty in assessing the long-term effects of pre-stres

induced deflection in full-continuity construction [BA 57/01]2).


Figure 5: Francis Case Memorial Bridge crosses the Washington Chan

of the Potomac River in Washington, DC [Telang and Mehrabi]3)

Additionally, the survey of using this bridge

construction approach in some American States

revealed that it could be accompanied with cracks ofunusual severity that can create a dangerous

situation. This may be clarified through the following

Bridge Case Study [Telang and Mehrabi]3).

The Francis Case Memorial Bridge, carries eight

traffic lanes over one channel of the Potomac River in

Washington, DC, connecting the downtown with

Potomac Park (Figure 5). In 1994 the approach spans

of this bridge were replaced with precast pre-stressed

concrete girders made continuous.




Figure 6: One of the larger cracks [Telang and M

In other words, by providing a large amount of positive moment

reinforcement at the diaphragms, makes the diaphragm area stronger

than the adjacent girder sections, thereby forcing the cracking to occurin far more critical but weaker areas of the girder span rather than in

the region of diaphragm [Telang and Mehrabi]3).

After four years, during a routine inspection, severe vertical cracks had been observed adjacent to th

intermediate support at Pier B on eight interior pre-stressed girders. The observed cracks were most

vertical, traversed the complete width of the bottom flange of the girder and, in some cases, traversed thfull girder height with the widest crack located at 1.4 m from the Pier (see Figure 6). Immediately all th

girders that were cracked or showed imminent potential for similar distress had been shored to ensu

safety of the structure. Then an in-depth research study had been initiated to ascertain the caus

prognosis and whether the structure could be repaired [Telang and Mehrabi]3).

Analytical investigation showed that the large positive moments generated on the Case Bridge that causin

tensile stresses and cracking at the soffit of girders at intermediate supports were due primarily to threstraint provided by the positive moment reinforcement in continuity diaphragm and the reduce

effectiveness of pre-stressing force at the end of the positive moment reinforcement within the girder cros

section, thereby creating an unusually weak section susceptible to

cracking under the applied moments.


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Modeling, Analysis and Design of Buildings AIT - Thailand ACECOMBridges Saudi Arabia 2013


Therefore, the design of the full continuity approach should be

attempted with caution for ensuring that the positive moment

connection at continuity diaphragms being designed and detailedsuch that any cracking, if it occurs, should be formed in the positive

moment region of diaphragm, rather than in the girder section [Telang

and Mehrabi]3). However, this may not normally be ensured.

It is worth mentioning that the four American States Florida, Georgia,

Minnesota, and Texas, based on their past experience, are not using

full continuity in the design for the precast pre-stressed concretegirder bridges [Chung C. Fu and Tarek Kudsi]6).

After experiencing difficulty in attaining continuity, spalling concrete

at the pier diaphragm, rotating at the end abutment (see Figures 7 and

8), Florida and Texas abandoned the practice of continuity and are

mainly designing simple span girder bridge [Chung C. Fu and Tarek

Kudsi]6), or using a simply supported girders supporting a

longitudinally continuous reinforced concrete deck over one to three

interior supports, the latter method, is currently the standard in Texas

[Scott Walton and Timothy E. Bradberry]4).

Figure 7: Cracking of the Beam and Diaphragm at Th

Intersection [Scott Walton and Timothy E. Bradberry

Figure 8: Severely Cracked Beam Ends at Continuity

Diaphragm [Scott Walton and Timothy E. Bradberry]4


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Figure 9: Partial Continuity Detail Method 1

Tied Deck Slab [BA 57/01]2)

Method 1: This method of partial continuity shown in

Figure 9, does not accommodate support rotations, there

is no moment continuity between spans and could be

susceptible to cracking. Separate bearings and end

diaphragms are provided for each span, tie reinforcementat mid-depth of the slab is debonded for a short length

either side of the joint to permit deck rotation.

Additionally, the slabs between spans are separated

using compressible joint fillers (but deck waterproofing

and deck surfacing are continuous) and special seals

are provided over the joint for double protection [BA

57/01]2) .

This type of continuity can be achieved over piers in bridge decks built using precast pre-stressed girder

by providing continuity in the deck slab only. BA 57/01

2)

describes the following two possible methods foachieving the partial continuity.

3.2 Partial Continuity Methods


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Figure 10: Partial Continuity Method 2, Contin

Separated Slab

Method 2: This method of partial continuity shown in Figure 10, is similar in concept to the continuity det

type 4, described by BA 57/012)

. In this method, first the girders are erected upon the ledge of the inverted

bent caps and the deck slab in each span will be casted separately and hence the bridge decks (at th

construction stage) will act as a series of simple spans.

3.2 Partial Continuity Methods (Contd.)

Then the connecting slab, as shown in Figure 10, shall be

casted after hardening of its adjacent deck slabs by a period

of time as maximum as possible, in order to mitigate

significantly the long-term effects of time dependent

deformation in the connecting slab. Therefore, the minimumallowable duration for the above described period of time and

the minimum girders age when casting the connecting slab

should be specified in the design drawings.

Additionally, the deck slab shall be separated from support

girders for a short length (debonding horizontal length

between vertical exterior edges of end diaphragms (as shownin Figure 10) using compressible material, in order to provide

rotational flexibility.


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This approach has been used successfully in Kingdom of

Saudi Arabia and it is worth summarizing its advantages:

This approach retains the simplicity and economy ofsimply supported construction whilst obtaining the

various advantages of deck slab continuity [BA

57/01]2).

The various relative rotations and deflections at the

support positions are accommodated within the

connecting slab elements and there is moment

continuity between spans.


Figure 10: Partial Continuity Method 2, Continuous Separate

Method 2 (Contd.): It is worth mentioning that the increasing of the aforementioned debonding lengt

reduces the stiffness of the connecting slab and consequently, reduces its restraint/continuity momen

However, the designer should carefully consider the instantaneous and long term effects of secondarstresses such as shrinkage, creep, thermal stresses, differential settlement, etc. (in terms of time an

construction schedule) in assessing design issues such as tension/compression and bending moment

developed in the connecting and in span slabs/ girders, bearing displacement, etc.


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Method 2 (Contd.):On the other hand, this method of partial continuity

has the following disadvantages:

The amount of additional longitudinal

reinforcement required in the slab/connecting

slab to handle the negative and positive moments

is significant/costly.

The providing of proper span for connecting slab

increases the eccentricity of bearing vertical

reactions against its supporting bent pier and

consequently additional amount of reinforcing

bars and concrete will be required.



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4. Showcasing the Design of Continuous Decks Over Simple Spans

Precast Pre-stressed Bridge GirdersA case study of Bridge spanning over a floodplain along the proposed expressway (M.O.T, KSA

connecting Al-Qassim Province with Makkah Al-Mukarramah, provides some guidelines anconsiderations that may be taken into account during the structural modeling and design of continuou

decks over simple spans precast pre-stressed bridge girders.

This case study bridge (as shown in Figure 11) carries eight traffic lanes and consists of (non-skewed

twelve equal spans of about 30 m, composed of simply supported girders supported on ledges o

inverted -T bent caps. Then each four spans are made continuous for superimposed / live loads throug

a continuous cast in place concrete decks.

Figure 11: Cross Section of Case Study Bridge


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4.1 Modeling Development

Figure 13: Proposed Continuity Detail

Figure 12: Girder Cross Section

Finite Element Models are used to investigate the most

probable responses of continuous decks over theaforementioned four simple-spans precast pre-stressed

(case study) Bridge girders due to vehicular live

loads/superimposed dead loads, time dependent material

behavior effects, thermal stresses, etc., using SAP 2000

software package. Accordingly, a proposed continuity

connection detail is presented and discussed.

The case Bridge of four continuous spans is composed of

23 Bulb Tee precast pre-stressed girders (see Figure 12)

in each span and constant girder spacing and span of

1710 mm and 27800 mm; respectively. Each girder is post-

tensioned with two 2240 mm2 tendons, with a jacking

force of 3130 kN per tendon and simply supported in both

ends on the ledges of inverted -T bent caps through steelreinforced elastomeric bearings (see Figure 13).


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4.1 Modeling Development (Contd.)

Then the four simple spans of girders are converted to continuous

spans through cast in place concrete slab of 200 mm thickness.

However, the girder top surface within the connecting slab region isdropped by 150 mm to allow increasing of the connecting slab

thickness to 330 mm and accommodating 20 mm thick of

compressible filler, as shown in Figure 13.

Expansion joints (see Figure 14) are provided at both ends of the

aforementioned developed four continuous spans.

Three-dimensional models are

utilized with proper refinement

of their components where

required as shown in Figure 15.

Figure 15: Finite Element Model (FEM) Plan

Figure 14: Proposed Expansion Joint De


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Therefore, each bearing is modeled using three spring elements distributed along transverse axis in

perpendicular to girder centerline and connected together with its associated girder end (frame

Element) by rigid link elements with their calculated fractional stiffness coefficients (see Figures 17and 18).

Figure 17: Modeling of Bearings (A Set of Rigid

Links and Springs)


Figure 18: Modeling Connection between Deck

Slab and Girder End Block


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In developing the Finite Element Models, the application of the following loads and environmental effects are

adopted:

Self-weight of Structure.

Superimposed Dead Loads. Vehicular Live Loads in accordance with M.O.T Highway Design Manual5).

Uniform Temperature (TU) and Gradient Temperature (TG) in accordance with M.O.T Highway Design Manual5) .

Differential Settlement of 25 mm of individual foundation in accordance with M.O.T Highway Design Manual5).

Time Dependent material behavior effects of concrete and tendons.

The Non-Linear Staged Construction Analysis has been adopted for the developed Finite Element Models in order to

investigate the effect of construction scheduling, aging, shrinkage and creep. However, the material and geometric

non-linearity are not considered and the following groups of elements, load patterns and load cases have beenadopted for defining the construction stages.


Groups

G1, G2, G3 and G4: for Girders in the first span through the fourth

span.

D1, D2, D3 and D4: for Diaphragms in the first span through the

fourth span.

S1, S2, S3 and S4: for Slabs in the first span through the fourth

Span.

L1, L2, and L3: for Connecting slabs throughout the four spans.

Load Patterns

TENDON: for pre-stressing applied to girders G1 through G4

GRAVITY 1: for self weight of girders G1 through G4.

GRAVITY2: for self weight of diaphragms in slabs S1 throug

GRAVITY3: forself weight of slabs S1 through S4.

GRAVITY4: for self weight of connecting slabs L1 through L

GRAVITY5: for superimposed dead loads

Vehicular Loads.

Temperature loads (TU and TG).

Settlement loads


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Load Cases

1. Load Case 1 (Starting from Zero Initial Condition) Add Girders G1, G2, G3 and G4 with an age 0 days

Add Bearing for G1, G2, G3 and G4.

Allow 10 days duration for aging and shrinkage.

2. Load Case 2 (Continue from State at End of Load Case 1)

Add Tendons

Apply Tendon Load to G1, G2, G3 and G4.

Apply Gravity 1 Load to G1, G2, G3 and G4.

Allow 05 days duration for aging, shrinkage and creep.


Add Diaphragms for G1 through G4 with an age 0 days.



Apply Gravity 2 Load to the Diaphragms.



Load Cases (Contd.)

5. Load Case 5 (Continue from State at End of Load Case 4) Add S1, S2, S3 & S4 with an age of 0 days.

Apply Gravity 3 Load to G1,G2, G3 & G4.

Allow 60 days duration for aging, creep and shrinkage.


Add L1, L2 and L3 with an age of 0 days.

Allow 14 days duration for aging, creep and shrinkage.


Apply Gravity 4 Load to Connecting Slabs.

Apply Gravity 5 Load to all.





10 Load Case 10 (Continue from State at End of Load Case 9)

Allow 3000 days duration for aging, shrinkage and creep.11. Load Case 11 (Continue from State at End of Load Case 10)

Apply vehicular loads (Maximum Positive Bending Moment)


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(Load Cases, Contd.)

12 Load Case 12 (Continue from State at End of Load Case 10) Apply Temperature Gradient (Maximum Positive Bending

Moments).

13 Load Case 13 (Continue from State at End of Load Case 10)

Apply Temperature Uniform (Maximum Positive Bending Moments).


Apply Differential Settlement (Maximum Positive Bending Moment).


Apply vehicular loads (Maximum Negative Bending Moment)16. Load Case 16 (Continue from State at End of Load Case 7)

Apply Temperature Uniform (Maximum Negative Bending Moment)


Apply Differential Settlement (Maximum Negative Bending

Moments)


However, additional load cases for modeling the effect of increasing the time period between casting of the connectslab and its adjacent in-span deck slab to 10 and 180 days have been investigated, then load combinations have b

also considered as appropriate.

Figure 19: TYPICAL LOAD CASE DESCRIPTION FOR STAGES


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4.2 Modeling Results and Discussions

The main results that can be extracted from the described Finite Element Models and that are of

interest for this study are:

Forces/moments in frame/shell elements

Top/bottom fiber stresses in shell elements

Forces/displacement/rotation in spring/node elements

However, the results and discussion herein will be concentrated on the structural performance of the

connecting slab under the aforementioned applied loads/displacement/temperature/construction

schedule.A space is not taken to provide the model results of the flexural moments and axial forces acting on

the connecting slabs, however, its combination effects may be reflected by their resulting top and

bottom fiber stresses.

Therefore, the output results in terms of the top and bottom fiber stresses of connecting slab are

selected as a compromise between accuracy and ease of study and comparison considerations. Theoutput results shall be denoted by their specified load case numbers as described in the model

development, unless otherwise specified.


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4.2 Modeling Results and Discussions (Contd.)

A. Material Behavior Time Dependent Effects: This effect may be described by the top and bottom fi

stresses of connecting slab as shown in Figures 20 through 23 (load cases nos. 7 and 10).

Figures 20 and 21 show the top and bottom fiber stresses; respectively, of connecting slab upon hardening and applying of the permanent loads, while Figures 22 and 23 showing (respectively) t

changing occurred in these fiber stresses in the long run (over 9 years) due to the effects of ti

dependent deformation caused by shrinkage and creep.

It can be noticed that the (instantaneous) maximum top fiber tensile stresses of 0.53 MPa and bottom fi

compressive stresses of -0.42 MPa, switch their places under the long-term effect of shrinkage and cre

and become -2.85 MPa (compression) and 3.25 MPa (tension); respectively.

Figure 20: Top Fiber Stresses of Connecting Slab at End of Load Case 7

Max. Stress = 0.53 MPa

Figure 21: Bottom Fiber Stresses of Connecting Slab at End of Load Cas

Max. Stress = -0.42 MPa


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Accordingly, for design purposes, the state of fiber stresses shown in Figures 20/21 and Figures 22/2

may be treated as the datum stresses for accumulating the extreme initial and long-term fiber stresse

respectively, resulting from other load cases.

In other words, the stresses resulting from load case causing tensile stresses on the top fiber

connecting slab to be added to the stress datum shown by Figures 20 and 21 (short-term effect), and t

stresses resulting from load case causing tensile stresses on bottom fiber of connecting slab to be adde

to stress datum shown by Figures 22 and 23 (long-term effect).

A. Material Behavior Time Dependent Effects (Contd.)






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B. Vehicular Live Loads Effect: This effect may be

described by the top and bottom fiber stresses of the

connecting slab shown in Figures 24 through 27 (LoadCases Nos. 15 and 11).

Figure 24 shows the maximum top fiber tensile

stresses of the connecting slab due to vehicular load

(that applied in the locations developing maximum

negative moments on the connecting slab) plus its

existing (instantaneous) fiber tensile stress due topermanent loads. It can be seen that the maximum top

tensile stresses has been increased from 0.53 MPa

(see Figure 20) to about 4.0 MPa. This increasing in the

tensile stresses in the connecting slab due to

vehicular loads is exceeding 6 times its existing

(instantaneous) tensile stresses due to permanentloads. While Figure 25 shows the corresponding

bottom fiber compressive stresses.

Figure 24: Top Fiber Stresses of Connecting Slab at End of Load Case


Figure 25: Bottom Fiber Stresses of Connecting Slab at End of Load Ca



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B. Vehicular Live Loads Effect (Contd.): Figure 27

shows the maximum bottom tensile stresses of the

connecting slab due to vehicular loads (applied on

the connecting slab span for developing maximum

positive moment on it) plus its existing (long-term)

fiber tensile stresses due to permanent loads. It

can be seen that the maximum bottom tensile

stresses has been increased from 3.25 MPa (see

Figure 23) to about 5.0 MPa. This increasing in the

tensile stresses in the connecting slab due to

vehicular loads is about 50% of its existing (long-

term) tensile stresses due to permanent loads.

While Figure 26 shows the corresponding top fiber

compressive stresses.



Figure 27: Bottom Fiber Stresses of Connecting Slab at End of Load Case



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C. Temperature Gradient Effects: This effect (based on the differential thermal gradient recommended b

M.O.T, KSA)5) causes tensile stresses in the bottom fiber of the connecting slab, and therefore has bee

added to the long-term stresses ofpermanent loads as shown in Figure 29 (at the end of load case 12and the corresponding top fiber compressive stresses as shown in Figure 28.

It can be seen that the maximum bottom fiber tensile stresses developed due to the effect of therma

gradient plus long-term effect of permanent load is increased from 3.25 to about 16.50 MPa that exceedin

the top and bottom tensile stresses resulting from the effect of vehicular live loads shown in Figures 2

and 27; respectively.






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D. Differential Settlement Effects: This effect of differential settlement of 25 mm (M.O.T, KSA)5), may b

described by the top and bottom fiber stresses of connecting slab shown in Figures 30 through 33 (End

Load Cases Nos. 17 and 14). As shown in Figure 30, the maximum top fiber tensile stresses developed duto the specified value of differential settlement (that develops negative moment on the top fiber of th

connecting slab) in the connecting slab plus its existing (instantaneous) fiber stress due to permane

loads, is increased from 0.53 MPa to about 2.50 MPa. This increasing in the tensile stresses due to th

specified differential settlement is exceeding three times the existing (instantaneous) tensile stresses du

to permanent loads and equals about 55% of the vehicular load effect (see Figure 24) . While Figure 3

shows the corresponding bottom fiber compressive stresses .






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D. Differential Settlement Effects (Contd.):

As shown in Figure 33, the maximum bottom fiber tensile stresses of connecting slab due to the specifievalue of differential settlement (that develops positive moment on the connecting slab) plus its long-ter

fiber stresses of permanent loads is increased from 3.25 MPa to 5.50 MPa. This increasing in the tensi

stresses in the connecting slab due to the specified differential settlement is about 70% of its existin

(long-term) tensile stresses due to permanent loads and exceeding the effect of vehicular load (see Figu

27). While Figure 32 shows the corresponding top fiber compressive stresses.






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4.2 Modeling Results and Discussions (Contd)

E. Uniform Temperature Effects (Contd.): As shown in Figure 37, the maximum bottom fiber tensil

stresses of the connecting slab after raising the uniform temperature by the specified value (plus it

existing long-term top fiber tensile stresses due to permanent loads) is increased from 3.25 MPa (se

Figure 23) to 3.50 MPa. This increasing in the tensile stresses in the connecting slab due to the specifieraising value of uniform temperature is about 7% of its existing (long-term) tensile stresses due t

permanent loads and equals about 14% of the vehicular load effect (see Figure 27).

It is worth mentioning that the uniform temperature applied could develop horizontal shear forces o

bridge deck elastomeric bearings and since the location of bridge bearings off the neutral axis of th

connecting slab, flexural moments in addition to axial forces will be developed in the connecting slab as

result of this loading.






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F. Effect of Time Period Between Casting of Connecting Slab and its Adjacent in-span Slabs: The top

and bottom fiber stresses shown in Figures 20 through 37 are based on allowing time period of 60 days

between casting of connecting slab and its adjacent in-span slabs and corresponding age of girders of

85 days when casting the connecting slab.

Figures 38 and 39 show the estimated top and bottom fiber stresses of the connecting slab due to the

long-term effects of permanent loads (over 9 years) when reducing the above described time period to

10 days and 35 days age of girders when casting the connecting slab; respectively.

On the other hand, the corresponding top and bottom fiber stresses of connecting slab due to long-

term effects of permanent loads (over 9 years) when increasing the aforementioned time period to 180

days (and corresponding age of girders to 200 days when casting the connecting slab) are shown in

Figures 40 and 41.

As can be seen from Figures 39 and 41, in the latter case, the maximum bottom fiber tensile stress of

the connecting slab has been reduced from 4.00 MPa to 2.30 MPa (about 43%). Therefore, increasing of

the above described period of time seems to be advantageous. This may be attributed to mitigation of

the long-term effects of time dependent deformation caused by shrinkage and creep.

Similarly, it may be concluded that the bottom fiber tensile stresses of connecting slab depends also on

the girder age at time of casting of connecting slab and it would be reduced with using older girder age.

4 2 M d li R lt d Di i (C td )


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F. Effect of Time Period Between Casting of Connecting Slab and its Adjacent in-span Slabs (Contd.):

Figure 38: Top Fiber Stresses of Connecting Slab at End of Load Case 10a




Figure 40: Top Fiber Stresses of Connecting Slab at End of Load Case 10b





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4 2 Modeling Res lts and Disc ssions (Contd )


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G. Top and Bottom Fiber Stresses of Connecting Slab Due to (Un-factored) Combination of Loads.

Figure 42: Top Fiber Tensile Stresses (Combination of Loads)


Figure 43: Corresponding Bottom Fiber Stresses (Combination of Loads


Figure 44: Bottom Fiber Tensile Stresses (Combination of Loads)


Figure 45: Corresponding Top Fiber Stresses (Combination of loads)



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G. Load Combination Results (Contd.):

And, the extreme (maximum) Bottom and top fiber stresses of the continuity slab using the above

mentioned Service (I) load combination but taken 100% of the force effects of Temperature gradient(when live load is not considered) are equal to 17.60 and -17.80 MPa, as shown in Figures 46 and 47;

respectively. It can be seen that the later combination of load is more critical.

In view of all the above, (for design purposes), it may conclude that the bottom fiber (tensile) stresses

of the connecting slab is more critical than its top fiber tensile stresses. This is an evidence that the

increasing of time period between casting of continuity slab and its adjacent in-span slabs (for

reducing the (long-term) bottom fiber tensile stresses (as shown in Figures 39 and 41) is advantageous.

Figure 46: Bottom Fiber Tensile Stresses (Combination of Loads)


Figure 47: Corresponding Top Fiber Stresses (Combination of loads)


4 3 P d C ti it Sl b C ti D t il


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4.3 Proposed Continuity Slab Connection Detail

Figure 48: Continuity Detail over Piers

A. Top Reinforcement: As shown in Figures 48

through 49, the negative moment connection

reinforcement of connecting slab shall be made

with the reinforcement protruded from its adjacentin-span deck slab ends (that has been already

casted and hardened) and extended (from both in-

span slab ends) throughout its full span, and

embedded there using 180o standard hook and

anchoring bar with a diameter equal to or greater

than the diameter of its negative moment

reinforcement.

The connecting slab connection detail has been proposed in view of its staged construction analy

results, the design provisions specified by AASHTO LRFD 20071) (for the positive and negative mom

connection reinforcement details of full continuity connection), and for ensuring that its top and bottreinforcement being adequately anchored/spliced with its adjacent deck slab/girder/end diaphra

reinforcement (in order to assure its full design capacity throughout its span).

4 3 P d C ti it Sl b C ti D t il (C td )


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4.3 Proposed Continuity Slab Connection Detail (Contd.)

Additionally, the aforementioned protruded negative

moment reinforcement shall be extended into the in-

span deck slabs, lap spliced with the deck slablongitudinal top reinforcement in compression zone

and its termination to be staggered.

B. Bottom Reinforcement: As shown in Figures 49 and

50, the positive moment connection reinforcement of

connecting slab shall be made using bottom

reinforcing bars extended throughout its span andembedded into its adjacent end diaphragms (within

the end diaphragm span region as shown in Figure

49) or supporting on the girder ends (within girder

width region as shown in Figure 50) using 180o

standard hook and anchoring bar with a diameter

equal to or greater than the diameter of its positive

reinforcement.

Figure 50: Continuity Detail over Piers (within girder width regio

Figure 49: Continuity Detail over Piers (within end diaphragm spa

4 3 P d C ti it Sl b C ti D t il (C td )


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4.3 Proposed Continuity Slab Connection Detail (Contd.)

Additionally, steel reinforcing bars equal in diameter and spacing to the positive moment connection

reinforcement of connecting slab shall be protruded from the girder ends (at the same level of

connecting slab bottom reinforcement as shown in Figures 48 and 50) and to be lap spliced with thebottom reinforcement of connecting slab.

These protruded reinforcing bars shall be extended into the precast pre-stressed girder and to be

(noncontact) lap spliced with its top reinforcing bars and their termination to be staggered in pairs

symmetrical about its centerline.

Figure 50: Continuity Detail over Piers (within girder width region)Figure 48: Continuity Detail over Piers


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5. Conclusions



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6. References



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