International Concrete Abstracts Portal

The paper investigates the shear strength and the failure modes of high strength concrete beams with and without steel fibers ( fC = 110 MPa). Sixteen reinforced high strength concrete beams (3600x350~200 mm) were tested under different combinations of shear force and bending moment. The beams were singly reinforced and without shear (web) reinforcement. The test results indicated that the addition of steel fibers to high strength concrete increases the ultimate shear strength, improves the brittle characteristic and transforms the failure mode into a more ductile one. The average gain of the ultimate shear strength due to the addition of steel fibers varied from about 14% to 14 1% depending on the shear span to depth ratio and the longitudinal steel ratio. Four modes of failure of reinforced high strength concrete are clearly distinguished as; diagonal tension, shear compression, shear flexure, and flexural failure. In general, cracks in fiber reinforced concrete beams are closer, narrower, and more than those in beams without fibers. This reflects the effect of steel fibers in redistributing the stresses beyond cracking.

This paper reports on the interventions carried out by the Middle East Technical University faculty and staff on the moderately damaged 120 buildings in Ceyhan, Turkey after the June 27, 1998 earthquake. Discussion includes the organization ofthe intervention as well as its stages. Paper includes results of some recent research carried out at METU laboratories on infilling frames and detailed analytical evaluation of the strengthening scheme applied on the buildings.

A numerical technique based on deformation compatibility and force equilibrium considerations is presented to predict the structural behaviour of continuous reinforced concrete beams strengthened with externally bonded carbon fibre reinforced polymer (CFRP) plates. Comparison between the behaviour predicted using the described method and experimental data shows good agreement. The technique was developed to predict hogging or sagging flexural failure in strengthened continuous beams but does not account for premature peeling failure. The influence of design variables such as the thickness, length and position of the external CFRP plates on the flexural capacity and the failure mode was also investigated. Increasing the external CFRP plate length decreases the probability of obtaining flexural failure next to the CFRP plate ends.

A new design capability for automated formulation of optimal truss models (strut-and-tie models) is presented and illustrated with example designs of a variety of disturbed regions of reinforced and pre-stressed concrete structures, including deep beams with holes, continuous beams, and comer joints. The design method selects the optimal geometry of the strut-and-tie layout, determining the proper positioning of tensile ties and compressive struts to minimize the amount of reinforcing steel needed in the tension ties of the truss model for the region being designed. Two practical parameters are under control of the design engineer running the computer program-a reinforcement layout practicality factor which can be used to force the reinforcement layout into strictly horizontal and vertical bars (which will require additional reinforcement volume beyond the true optimal value), and a stress redistribution factor which can be used to control the amount of redistribution needed in developing the full capacity of the truss model after cracking has occurred.

There is an ever increasing need to strengthen concrete structures due to deterioration, construction errors, environmental effects, occupancy changes, design flaws and other reasons related to the structure. Externally applied carbon fiber reinforced polymer (CFRP) strips and sheets can be used to strengthen these structures. This technique offers many advantages to conventional methods such as being cost effective, ease of handling and allowing minimal impact to the structure. This paper presents a case study of the strengthening of a critical research facility using CFRP. It was imperative that the repair and strengthening did not impact the ongoing research in the !faciIity in any way. Preliminary testing and structural considerations of the damaged and deteriorated portions of structure are presented. In addition, this paper presents the results of a comprehensive post-strengthening testing program performed on the repaired facility. Non-Destructive Testing (NDT) techniques such as full-scale load testing, vibration analysis, and infrared thermography used to evaluate the repair process are presented and shown to be proven methods of verifying the application of the CFRP.