Fiber Reinforced Concrete Joints for Precast Construction in Seismic Areas

Khaled  S. SOUBRA

 It is the purpose of this study to combine the use of precast concrete with fiber reinforced cast‑in‑place concrete in beam-to-column connections to provide a better, safer, and more economical design. This research will also investigate moving the plastic hinge, in other words, moving the connection between the precast elements away from the face of the column. At that location, the design requirements such as ductility, strength, and energy dissipation would be provided by the cast‑in‑place fiber reinforced concrete connection. The study was divided into four major parts. The objectives and scope of each part are as follows:

 The first part of the investigation involved the selection of a suitable fiber reinforced concrete matrix to be used as the cast-in-place connector material between the precast elements. This connector had to have the characteristics mentioned before such as strength, ductility, and energy dissipation. To achieve this purpose, thirty-nine fiber reinforced concrete cylinders were tested in compression. The mixes in the cylinders were varied, covering a wide variety of fiber types, lengths, aspect ratios, and volume fractions. Data from the compression tests was collected and matrices with adequate strength, toughness, and ductility were selected for use in the second part of the investigation.

 In the second part of the investigation, six beam‑type specimens were tested, each consisting of two precast concrete parts joined together by a cast‑in‑place joint. The objectives were: 1‑ To verify the adequacy of the selected fiber reinforced concrete matrices in bending, 2‑ To verify their ability to provide the required strength, ductility, and energy dissipation to the specimens, 3‑ To verify the adequacy of the reinforcing arrangement inside the cast‑in‑place joint.

 The beam specimens were tested under cyclic third point loading to simulate earthquake conditions. The test results were used as guidelines for the third part of the investigation.

 In the third part of the investigation, four beam-column subassemblages were tested, each consisting of two precast concrete parts joined together by a cast‑in‑place joint. The objectives were: 1‑ To verify the adequacy of the selected fiber reinforced concrete matrices in bending and shear, 2‑ To verify their ability to provide the required strength, ductility, and energy dissipation to the subassemblages, 3‑ To verify the adequacy of the reinforcing arrangement inside the cast‑in‑place joint.

 The subassemblages were put in a testing frame and subjected to load reversals. Data collected from the test was used for comparison with results from the analytical study in the last part of the investigation.

 In the last part of the investigation, an analytical study was undertaken to: 1‑ Propose an analytical model to simulate the behavior, under load reversals, of beam‑column connections between precast concrete elements, 2‑ Verify the accuracy of such a model, using the available data from the experimental investigation, 3‑‑ Propose recommendations for the design of connections between precast concrete elements in seismic areas.

 To achieve this purpose, the beam‑column subassemblages were modeled analytically. DRA1N‑2D, a dynamic response analysis program was then used to analyze the inelastic behavior of the subassemblages. After achieving a satisfactory representation of the behavior, a multistory multibay structure was analyzed to study the effectiveness of fiber reinforced concrete joints in resisting earthquake loads as compared to monolithic construction.