Live Experimental Test
Thursday, October 29, 2009, 1:30 PM (PDT)
Specimen Design and Testing Piles Extension Connection to Slab Bridges
FSRCC24 (Modified) - Experiment
Previous Experiments - FSRCC24 - DCKJ24 - FSKJ24
PI
David Sanders, Professor, Civil and Environmental Engineering
Graduate Research Assistant:
Mohamed Ayoub
Sponsored by
California Department of Transportation (CalTrans)CalTrans Project Monitor:
Dr. Ahmed Ibrahim
Dr. Saad El-Azazy
ABSTRACT
Slab bridges are structures where the pile works as a pile under the soil level and as a pile above the soil level. The pile is then directly connected to the superstructure. The California Transportation Department (CALTRANS) has a large number of highway bridges; and many of them are slab bridges. Although slab bridges are common type of bridge, the current version of the Bridge Design Specification (BDS) and the Seismic Design Criteria (SDC) provide limited design guidance for pile extension connection details for slab bridges. Unlike the pile to box-girder bridge connections which are under extensive discussion and have been extensively tested, slab-bridge connections have not been tested.
Eight large scale pile-slab bridge connections are the target of the research; six specimens have already been tested. The current specimen was designed based on the experimental results and the Strut-and-Tie Model for the forth specimen (FSRCC24) Constant axial load (76.5 kips) will be applied to the specimens while it is subjected to lateral load reversals with increasing drift levels.
Specimen Selection and Details
The embedded length of the pile varies according to the soil type. In the plans submitted by Caltrans to UNR, the height of the pile above the ground ranged from 9D to 20D. Therefore, an average height of the pile above the soil surface equals 14.5D. The point of the maximum moment for the individual pile can be approximated at D to 2D under the surface of the soil. This increases the average total length to 15.5D to 16.5D. The pile inflection point will be approximately halfway between pile top and maximum moment point in the soil. Piles with shear lengths greater than 6D are considered flexural members. Therefore, the height of the specimen was chosen to be 6D.
The reinforcement of the current specimen was designed based on the experimental results and the Strut-and-Tie Model for the forth specimen (FSRCC24). The reinforcement details for the new and old design are shown in Figure 1 and Figure 2 in the Handout, respectively. The most significant changes in the steel details for the new design are:
- In the longitudinal and transverse direction of the joint additional 5#8 bars were added in the top and bottom side of the joint as shown in Figure 1. The additional steel for the top and bottom reinforcement of the slab will be added in the range of (D+2ft), which is the minimum effective width of the joint.
- For vertical joint, 24 # 6 J-dowels were added to transfer force from longitudinal reinforcement of the pile to the longitudinal reinforcement of the slab.
- Additional stirrups on the pile face, 2 #6 two legged stirrups were added for each side of the pile in distance equals to Bcap=Dc+2 (ft) = 24+24=48-in.
Test Setup
The transfer of axial loads to the specimen was accomplished through a steel Ibeam that was placed across the pile top. The test is conducted in an inverted position; so the lateral force will be applied to the top pile and the slab placed at the bottom during test as shown below.
Handout:
A handout describing the test can be downloaded here: Download Handout
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