Pedro Franco Silva

Rehabilitation of Compression Steel Members Using FRP Pipes Filled with Non-expansive and Expansive Light-weight Concrete

This paper presents the experimental and analytical evaluation of the feasibility of a proposed fiber reinforced polymer (FRP) retrofit method to strengthen corroded steel columns. This method consists of two steps: (1) wrapping the corroded steel column with an FRP jacket, and (2) filling the jacket with expansive light-weight concrete. Seven steel columns were tested in the laboratory including five strengthened columns with the proposed technique. The first two were used as control units where one was a virgin shape and the second was notched in the center zone to simulate the loss of section due to corrosion. The remaining five were all notched, and confined with FRP composite pipes within the simulated corroded zone and subsequently filled with light-weight concrete. All specimens were axially loaded to failure while strain and displacement readings were measured to demonstrate the feasibility of this repair concept. Test results show that the proposed FRP retrofit method for steel columns can be successfully applied. Furthermore, an analytical model was developed that can predict the load capacity of the FRP retrofitted steel column.

Seismic Performance of Sacrificial Interior Shear Keys

Experimental and analytical results from a research program conducted to evaluate the seismic performance of sacrificial interior shear keys are presented. The program consisted of 7 experiments under which several variables were investigated: 1) loading protocol; 2) geometry; and 3) reinforcement ratio. These experiments provided results that were used to develop rational models of the force and deformation capacity of sacrificial interior shear keys as well as their postpeak performance under cyclic loads. Test results show that in their current form, existing design methodologies underestimate the capacity of sacrificial interior shear keys and a more comprehensive design procedure must be implemented. Based on experimental results, a detailed analytical investigation of the sacrificial shear keys was conducted and findings are provided herein.

A THEORETICAL STRATEGY FOR MOMENT REDISTRIBUTION IN CONTINUOUS FRP-STRENGTHENED CONCRETE STRUCTURES

The use of fiber-reinforced polymer (FRP) composites is now a widely-accepted solution for the strengthening of reinforced concrete structures. FRP strengthening schemes offer many well-documented benefits for the retrofit of many existing concrete buildings and bridges. However, the main drawback in using FRP for such purposes is the reduction in ductility that the strengthened structure displays after strengthening. This loss in ductility has led various design guidelines around the world to prohibit any redistribution of bending moments in continuous FRP-strengthened concrete structures. This means that continuous structures, which might have been designed originally under assumptions of moment redistribution, should be designed for FRP strengthening according to elastic distribution of bending moment. This could lead to onerous conditions for such strengthening schemes, particularly in hogging regions. This paper sets out a rationale for the possible appropriate use of redistribution principles for FRP-strengthened concrete.

PERFORMANCE OF SACRIFICIAL EXTERIOR SHEAR KEYS UNDER SIMULATED SEISMIC LOADING

This paper presents a performance evaluation of sacrificial exterior shear keys under simulated seismic loading. Performance evaluation was conducted in terms of damage levels observed during testing. The experimental program consisted of 6 experiments, and the variables investigated during testing are outlined and discussed. The results of the evaluation are used to make realistic assumptions of the load-deformation response of sacrificial exterior shear keys as well as their postpeak performance under cyclic loads. Experimental and analytical results are also used to develop a hysteretic model for exterior sacrificial shear keys at the abutments. The development of this hysteretic model is also detailed.

Prediction of Blast Loads Based on the Expected Damage Level by Using Displacement Based Method

This paper describes how the equivalent viscous damping (EVD) ratio is a crucial parameter in the application of the displacement based method. Previous works have correlated the EVD ratio as a function of the displacement ductility level based on the hysteric response of reinforced concrete members subjected to blast loads. Furthermore, the displacement response factor (DRF) for blast loads was proved as a function of the EVD ratio and the ratio of impulse duration to the natural period. The explosive charge weight and stand-off distance required to impose a given damage level were predicted by the DBD method based on these research results. In order to examine the feasibility of assessing the blast-resistant capacity of concrete (RC) slabs using the displacement based design (DBD) method. A RC slab was tested under real blast loads in the out-of-plane direction. Test results have shown that the blast loads were effectively estimated and the damage levels observed from the field tests correlated well with the predicted levels.

Innovative mechanical device for the post-tensioning of glass fiber reinforced polymer bars for masonry type retrofit applications

A mechanical device specially designed for the application of low-level post-tensioning forces to glass fiber reinforced polymer (GFRP) bars has been developed at the University of Missouri-Rolla. Some of the advantageous features of this device are that it is simple to assemble and the low-level post-tensioning forces can be applied manually and safely without the need for hydraulic jacks or heavy equipment. This device has been conceived with the main objective of retrofitting masonry buildings, some of which remain in service despite large, open cracks leading to considerable instability and serviceability concerns. According to the method derived in this paper, GFRP bars are installed in artificially imposed grooves and then post-tensioned with low-level stresses with the main objective to partially close these cracks, such that the serviceability and in-plane capacity of un-reinforced masonry (URM) buildings may be regained. In this paper we describe the mechanical components of this device, along with its advantageous features and potential application for the retrofit of URM walls.