Structural Behavior of Full Scale Totally Precast Concrete Counterfort Retaining Wall System
thesisposted on 07.03.2017, 00:00 authored by Maen A. Farhat
Totally Prefabricated Concrete Counterfort Retaining Wall (TPCCRW) provides an alternative for conventional construction techniques to reduce the drawbacks associated with cast-in-place construction. TPCCRW is composed of a precast concrete wall component (face panel and counterforts) and a base slab connected, on-site, through headed anchors. The anchors extend downward from the counterforts into shear pockets located in the precast base slab. While the structural design of TPCCRW shares some features with cast-in place systems, it also has specific requirements for anchor connections, strength of shear pockets, and counterfort design. The design of TPCCRW was developed according to AASHTO LRFD (2012) specifications and compared to an existing cast-in-place counterfort system in Chicago, IL, for both structural and economic performances. The design strength of TPCCRW (moment and shear) surpassed that of the existing system with an overall reduction in concrete volume of 57%. A parametric study identified a counterfort spacing-to-base length ratio of 0.35 and a counterfort extension-to-heel length ratio of 0.6 as optimal values. In addition, the overall structural behavior of TPCCRW was examined experimentally and analytically using Nonlinear Finite Element Analysis (NLFEA). A full scale prototype (20 ft 2 in. high and 13 ft 10 in. wide) was designed meeting the requirements of AASHTO LRFD specifications, assembled, constructed, instrumented and tested at the precast concrete plant. The design was optimized and validated using NLFEA. The precast components were connected through five headed anchors at each counterfort. The results showed that the wall experienced a deflection of 0.2 in. at its middle. The anchors succeeded to maintain serviceability and ultimate strength requirements. The proposed system required a unique method of construction. Therefore, the fabrication and construction procedures and guidelines required to accelerate the erection process on site were detailed. The system components can be fully assembled and set in place in less than 2 hours. Finally, the pullout behavior of headed anchors used in TPCCRW was examined experimentally and analytically using NLFEA. Eighteen precast concrete blocks (21 in. x 20 in.) having a truncated shear pocket identical to those used in TPCCRW were prepared, grouted with headed anchors, instrumented, and experimentally tested. The study took into consideration two different block thicknesses (14 in. and 6 in.), two IDOT certified types of headed anchors and types of concrete grout, different bar sizes (#6, #7, #8, #9), and different embedment depths (12.5 in., 10 in., 8 in, and 6 in.). The structural behavior of the pullout specimens was characterized by yielding and fracture of steel anchors regardless of their size. Concrete breakout was witnessed in 14 in. thick concrete specimens made with #9 headed anchors and 6 in. embedment depth when the specimen was tested to ultimate. The experimental test results were verified using finite element analysis and compared to design codes and other studies in the literature. The result showed close correlation with the AISC design guide for base plates and headed rods.