Tarek Alkhrdaji

Performance of Double-T Prestressed Concrete Beams Strengthened with Steel Reinforcement Polymer

In the fall of 2002, a two-storey parking garage in Bloomington, Indiana, built with precast prestrestressed concrete (PC) double-T beams, was decommissioned due to a need for increased parking-space. This led to the opportunity of investigating the flexural performance of the PC double-T beams, upgraded in the positive moment region with steel reinforced polymer (SRP) composite materials, representing the first case study where this material has been applied in the field. SRP makes use of high-strength steel cords embedded in an epoxy resin. This paper reports on the test results to failure of three beams: a control specimen, a beam strengthened with one ply of SRP and a third beam strengthened with two plies of SRP anchored at both ends with SRP U-wraps. Results showed that SRP can significantly improve both flexural capacity and enhance pseudo-ductility. Preliminary analytical work shows that the same approach used for externally bonded fiber reinforced polymer (FRP) can be satisfactorly used for SRP.

Upgrading Missouri Transportation Infrastructure: Solid Reinforced-Concrete Decks Strengthened with Fiber-Reinforced Polymer Systems

More than 40 percent of the bridges in the United States need repair, strengthening, or replacement. Because of limited funds, many states are forced to post load restrictions on their bridges as a temporary measure. Recently, fiber-reinforced polymers (FRPs) have emerged as a practical solution for repair or strengthening of highway bridges. Since there are no nationally accepted specifications for design and construction with bonded FRP reinforcement, the Missouri Department of Transportation (MoDOT) has funded a research program aimed at validating the design and analysis procedure through strengthening and testing to failure of bridges under realistic highway loading and conditions. Two bridges, Bridge G270 and Bridge J857, were selected for this demonstration. Both bridges are solid reinforced-concrete (RC) slab bridges. Bridge G270 was strengthened to increase its load-carrying capacity by using externally bonded carbon FRP and is still in service. Two of the three deck slabs of Bridge J857 were strengthened with FRP composites. Elastic tests were conducted on Bridge G270 before and after strengthening. Laboratory and field tests were conducted to validate the analytical model and design capacity. The decks of Bridge J857 were tested to failure under static loads. Test results indicate that strengthening with FRP can increase the capacity of solid-slab bridge decks. Strength and failure modes can be predicted by using the classical approach for RC design and analysis, based on equilibrium and compatibility. The research program, strengthening techniques, test results, and modes of failure of the bridge decks tested are reported.

In-Situ Load Testing: A Theoretical Procedure to Design a Diagnostic Cyclic Load Test on a Reinforced Concrete Two-Way Slab Floor System

The objective of this paper is to showcase to an engineer who is considering performing a diagnostic cyclic load test a theoretical procedure for determining the patch load, which when applied to a two-way reinforced concrete (RC) slab floor system would generate internal forces at critical locations equal to those resulting from the uniformly distributed load. This procedure should also help the practitioner to define a representative model of the structure and to update the magnitude of the target load at the end of each loading and unloading cycle by means of a real-time evaluation of boundary conditions and slab stiffness. The routine to design a cyclic load test is described theoretically first and then validated with the results of a load test on a concrete two-way RC slab floor system. Introduction The current role of testing within structural engineering has gained increasing importance, as it can now be applied to every phase of the structure’s life because of innovative materials and new design approaches. By focusing on either the preliminary testing of a new structure or the necessary control checks prior to assessing the strength of an existing one, in-situ load testing can determine the real behavior of the structure under the existing loading conditions. Accordingly, researchers can have an overall, accurate understanding of the mechanical properties of the structural members. In the United States of America, the current American Concrete Institute (ACI) 318 Building Code [1] provides requirements for load testing of concrete structures. ACI Committee 437 [2] proposes a diagnostic cyclic load (DCL) testing procedure consisting of the application of patch loads in a quasi-static way to the structural member according to loading and unloading cycles. Patch load magnitude and distribution shall simulate the uniformly distributed load defined in the ACI 318 Building Code. The DCL protocol [3,4] defines three acceptance criteria that can be easily computed, in real time, for any structural member by simply checking its behavior under the test load (see Fig. 1 for necessary notation). Repeatability and Permanency represent the behavior of the structure during two identical load cycles; Deviation from linearity represents the measure of the nonlinear behavior of a member being tested. Repeatability = 100 95 B B max r A B max r % % Δ − Δ × ≥ Δ − Δ ; (1) Permanency = 100 10 B r B max % % Δ × ≤ Δ ; (2)

REHABILITATION OF 120 INCH PCCP AT A NEW MEXICO POWER PLANT USING CFRP AND STRONGPIPE HYBRID FRP SYSTEMS

Internally bonded fiber reinforced polymer (FRP) composite liners have been successfully used to rehabilitate damaged and deteriorated prestressed concrete cylinder pipes (PCCP) since early 1990s. These systems consist of multiple layers of longitudinal and circumferential FRP sheets that are saturated on site with epoxy and installed using manual wet lay-up process to produce a cured-in-place composite pipe within the existing pipe. FRP liners have gained popularity as they do not require excavation and can be installed in a relatively short time. However, these systems are relatively expensive and are more suited for individual and short runs of pipes. A more cost effective solution for pipe habilitation can be achieved using a hybrid steelFRP rehabilitation system. The system consists of high strength steel wires continuously wrapped inside the pipe and embedded in a high performance polymeric matrix. The steel wires are placed between two layers of FRP to produce a sandwiched composite structure. The hybrid system combines the stiffness, ductility and low cost of steel with the durability and excellent performance of FRP to produce a structural liner with bidirectional strength that can be used for repair and renewal of both short and long runs of pipes. This paper presents a case study for the rehabilitation of 120 in. (3.05 m) diameter PCCP in a power generation facility located in New Mexico. Both carbon FRP (CFRP) and Hybrid FRP systems were used to upgrade the deteriorated pipe sections. The CFRP system was installed in the discharge line while StrongPIPE Hybrid FRP system was installed in the intake line. The paper highlights the features, limitations, feasibility, quality control requirements and cost of the two rehabilitation systems.

THE DEVELOPMENT OF A NOVEL STEEL REINFORCED COMPOSITE (SRC) LINER FOR THE REHABILITATION OF DETERIORATED PCCP

This paper presents details for the development of an innovative steel reinforced composite (SRC) system used for prestressed concrete cylinder pipes (PCCP) remediation. SRC system is a trenchless technology that consists of high strength steel wires continuously wrapped inside the pipe and embedded in cementitious or polymeric matrix. The system was designed to address shortcomings of current PCCP remediation techniques such as replacement, cured-in-place pipe CIPP, slip lining, and jacketing with fiber reinforced polymers (FRP). Full scale pressure testing was performed on two 1676 mm (66 in.) diameter PCCP sections, with and without the SRC system. Part or all of the existing pre-stressing wires in the host pipes were cut to simulate the behavior of a damaged PCCP during the test. Results indicate that while the unstrengthened pipe failed at a low pressure with partial wires cut, the SRC system was able to restore 100% of the original design capacity of the host pipe with 100% of the original prestressing wires cut. SRC design procedure, full scale pressure tests and results, and final conclusions are included in this paper.

The Design and Construction Considerations for PCCP Rehabilitation Using FRP Composites

Strengthening of Prestressed Concrete Cylinder Pipe (PCCP) using externally and internally applied fiber reinforced polymer (FRP) jackets has been successfully used since the early 1990’s. FRP composites are high strength, non-corrosive and durable materials and can add considerable structural capacity which makes them very suitable for PCCP strengthening. However, there are key material, design, and construction issues specific to PCCP rehabilitation that lack consensus within the industry. They include conditioning of the pipe prior to FRP installation, minimum material durability requirements, FRP stress limits for design and the level to which it can be designed to work compositely with the existing pipe or as a stand alone liner. For example, the condition of the pipe inner concrete coating can significantly affect the installation process. Dehumidification, surface repairs and preparation are critical for achieving durable pipe rehabilitation. In addition, the method of providing a watertight end termination detail for the FRP liner is key to ensuring proper performance of the composite liner.

In-Situ Evaluation of Structures Using Load Testing

In-situ load testing is commonly used to assess the safety or the serviceability of an existing or new structural system or part of its elements for a particular external load condition. The most frequently used load testing procedure includes the in-situ load test method described in Chapter 20 of the ACI 318 - Building Code Requirements for Structural Concrete and the Cyclic Load Test method in ACI 437 and ACI 437.1R. This paper describes the load testing programs used for two field projects to evaluate the load capacity of existing and upgraded structural components. The main objective of this paper is to describe the process for determining the test load level, loading procedure, instrumentation, evaluation criteria and load test outcomes. The first case study is for the evaluation of the sidewalks for a historical steel bridge in which the supporting beams lost up to 70% of the original crosssection due to extensive corrosion. The load test was performed in order to assess whether the sidewalks were able to safely support the pedestrian load. The second case study is for the evaluation of a typical bay in an old reinforced concrete (RC) pan-joist floor system. The floor was being considered to support new telecommunication equipment that required an increase in the capacity of the floor system. Load tests were performed for typical existing members and members upgraded using externally bonded FRP reinforcement as well as bonded RC overlay.