Riyad S. Aboutaha

Retrofit of Concrete Columns with Inadequate Lap Splices by the Use of Rectangular Steel Jackets

This paper describes an experimental research program on the use of rectangular steel jackets for seismic retrofit of non-ductile reinforced concrete frame columns. Eleven large scale columns were tested to examine the effectiveness of various types of steel jackets for improving the ductility and strength of columns with an inadequate lap splice in the longitudinal reinforcement. Response of the columns before and after being strengthened with steel jackets was examined. Several types of steel jackets were investigated, including rectangular solid steel jackets with and without adhesive anchor bolts. The test results indicate that a thin rectangular steel jacket combined with adhesive anchor bolts can be a highly effective retrofit measure for reinforced concrete columns with an inadequate lap splice. Design guidelines for the use of rectangular steel jackets as a seismic retrofit for non-ductile reinforced concrete columns are presented.

Environmental Reduction Factors for GFRP Bars Used as Concrete Reinforcement: New Scientific Approach

This paper presents a new approach that incorporates the effects of temperature, design life, and relative humidity (RH) of exposure into the environmental reduction factor (RF) for glass fiber reinforced polymer (GFRP) bars used as concrete reinforcement. The environmental RFs for GFRP bars that are adopted in various guidelines are presented and discussed. By using time extrapolation and time-temperature shift approaches, a new equation for design strength of GFRP bar under various exposure time and temperature was proposed. The effect of moisture, in the form of RH, was incorporated into the new equation by investigating the degradation mechanism of GFRP bar owing to alkali attack and the relationship between the RH and concrete pore water. Design examples for strength RFs linked to service life, temperature, and RH were presented on the basis of reported durability data for E-glass/vinyl ester (VE) GFRP bars embedded in concrete.

Seismic resistance of steel confined reinforced concrete (SCRC) columns

SUMMARY Tall building columns are subjected to high axial loads particularly at lower levels. In zones of high seismicity, these columns have to maintain their axial load carrying capacity during an earthquake. Conventional ordinary reinforced concrete, structural steel and concrete filled tube columns are not as effective as steel confined concrete columns. Steel tubed concrete columns are more ductile and have higher lateral resistance even under high axial compressive loads. In this paper, the seismic behavior of steel confined reinforced concrete columns is presented. Results were compared with those of ordinary reinforced concrete columns. The test results suggest that steel confined reinforced concrete columns are more ductile and have better seismic performance than ordinary reinforced concrete columns.

Development of interim recommendations for improved welded moment connections in response to the northridge earthquake

Publisher Summary A short-term research and testing program is conducted in response to damage observed at a large number of welded steel moment connections following the 1994 Northridge Earthquake. The test program investigated several changes to joint welding and design procedures intended to improve earthquake response of steel moment frame connections. Sixteen very large scale beam-to-column connections are tested under cyclic load. The most successful connections tested in this program are those in which the beam flanges are reinforced with cover plates or vertical ribs. The test results showed that reinforcing the connection to reduce stress at the beam flange groove welds, combined with reasonable care in welding can significantly enhance joint performance. The results of this test program suggest that improved welding workmanship, by itself, may not be adequate to assure satisfactory performance of the conventional welded flange-bolted web connection detail under inelastic cyclic loading. The results also indicate that a large improvement in cyclic loading performance is possible at steel moment flame joints by the use of a reinforced connection combined with careful attention to welding.

Flexural Strength of Corroded Lap Spliced RC Bridge Column Section

Reinforced concrete (RC) bridge columns with inadequate lap splices in the longitudinal reinforcement are very vulnerable. They are even more critical in corrosive environments. Corrosion of steel bars decreases the steel section, reduces ductility, and deteriorates the bond between the steel reinforcing bars and the surrounding concrete. The base of a bridge pier, where the main reinforcing bars are lap spliced with starter bars, is a bond-critical region in RC bridges. This paper presents a model for estimation of the stress at corroded lap-spliced bars for tension-controlled RC column sections. The amount of stress in the steel bars at the ultimate limit state was estimated based on the experimental data of bond stress between the steel bars and concrete. Using the bond strength of corroded and non-corroded steel bars, stress of corroded lap-spliced bar is expressed in terms of corrosion rate and the original yielding strength. The results of this investigation suggest that corrosion of lap-spliced steel bars has significant impact on the load transfer between the lap-spliced bars and, consequently, drastic decrease in the flexural capacity of bridge columns.

Finite Element Analysis of Cable-Stayed Strands’ Failure Due to Fire

The failure of one structural element may lead to the failure of the other structural components where ultimately result in the collapse of the large sections or the entire structure. The progressive collapse of the structures have been mainly investigated for buildings. However, cable failure in cable-stayed bridges may cause catastrophic consequences due to the progressive collapse. This is also crucial in part given the importance of bridge infrastructure in transporting people and the goods across the country and the key role that they play in contributing towards the nation’s economy. In design process of the cable-stayed bridges, the possibility that the loss of one cable might be leading to the collapse of the entire structure is often overlooked. This is particularly due to the structural redundancy considerations and the high safety factors in design of the structural components for these bridges. In this paper, the effects of a hypothetical fire and the thermal gradient propagation along a pre-stressed cable is studied using non-linear finite element modeling and analyses. For this purpose, the possible fire intensities and durations are studied in order to determine their effects on the strength losses in pre-stressed cables using finite element method. Results of this research could be used as basis for investigation of structural failure of cable-stayed/suspended systems.

Seismic Performance Study on the Joint of Crisscross Concrete-Filled Steel Tube Column-Steel Beam in Different Axial Compression Ratios

In this paper, the finite element analysis software ABAQUS is used to study the seismic performance of the joint of crisscross concrete-filled steel tube core column-steel beam tested by the pseudo static simulation under low cyclic loading. Then we can get the load-displacement curves of the joint when the axial compressive ratios are 0.2~0.9. By the data analysis can be drawn: the joint of crisscross concrete-filled steel tube core column and steel beam has good ductility and strong plastic deformation capacity, and it can absorb the seismic energy largely; within range of smaller axial compression ratios, the ultimate bearing capacity of the joint has increased with the increasing of axial compression force, however, in range of larger axial compression ratios, the ultimate bearing capacity of the joint has reduced with increasing of the axial compression force; and ductility of the beam-column joint has no obvious decline when the axial force increases.

Effects of Beam Material Strength on the Seismic Performance of Composite CFST Column and Steel Beam Connection

Composite concrete filled steel tubular (CFST) column is a new type of column having high ductility and high load-bearing capacity. In this paper, the finite element analysis software ABAQUS is used to study the seismic performance of 3D joint of composite CFST column and steel beam. The hysteretic curve and skeleton curve are obtained by changing the strength grade of the steel beam; calculate the energy dissipation ratio of the joint. The results show that the higher the beam’s steel strength the higher ultimate capacity of the joint in the constant axial load. But the full degree of hysteresis curve, energy dissipation and displacement ductility of the space joint decrease.