International Concrete Abstracts Portal

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.

In the late 1990’s stainless steel has gained increased acceptance as an economically viable material for concrete reinforcement in bridge decks. Its ease of fabrication and outstanding resistance to corrosion caused by chlorides and other corrosive effluents have allowed it to be used in new bridge construction as well as rehabilitation projects. Corrosion studies have indicated that the material may have easily a life cycle of between 50 and 100 years even with heavily salted highways. Additions of nitrogen and special processing have also allowed the project designers to save weight and reduce the use of special membrane layers and other concrete additives to the bridge design. This therefore in part defrays the higher initial cost of using stainless steel reinforcement as compared to either epoxy coated or plain black steel. Before 1995, several projects in the USA, the UK and in Europe had employed 304 grade stainless as reinforcement. In North America in the last several years, higher-grade alloys of stainless such as 3 16LN and Duplex 2205 have been used more prevalently. This paper will examine the benefits of the use of these alloys. We will address why they have become increasingly accepted as well as the reasons for their selection in specific bridge projects in North America. We will also examine the specific role of moly and nitrogen as alloying elements in stainless steel rebar. A general review of corrosion mechanisms, potential problems and the physical and mechanical properties of these alloys as compared to other potential alloy selections will also be presented.