Adolfo B. Matamoros

Update to ASCE/SEI 41 Concrete Provisions

A proposed supplement to ASCE/SEI 41 Seismic Rehabilitation of Existing Buildings has been developed for the purpose of updating provisions related to existing reinforced concrete buildings. Based on experimental evidence and empirical models, the proposed supplement includes revisions to modeling parameters and acceptance criteria for reinforced concrete beams, columns, structural walls, beam-column joints, and slab-column frames. The revisions are expected to result in substantially more accurate and, in most cases, more liberal assessments of the structural capacity of concrete components in seismic retrofit projects.

DESIGN OF SIMPLY SUPPORTED DEEP BEAMS USING STRUT-AND-TIE MODELS

This paper presents a procedure for calculating the amount of reinforcement and strength of deep beams based on strut-and-tie models. The proposed design equations were calibrated using experimental results from 175 simply supported beams found in the literature with a maximum shear span-to-depth ratio of 3. The strength reduction coefficient for concrete in the main strut was found to decrease with the angle of inclination of the strut, resulting in lower values than those stated in Appendix A of the 2002 ACI 318 Building Code for beams with shear span-to-depth ratios greater than 1.

EXPERIMENTAL EVALUATION OF DESIGN PROCEDURES FOR SHEAR STRENGTH OF DEEP REINFORCED CONCRETE BEAMS

This paper gives results from monotonic testing of 4 reinforced concrete deep beams. The behavior of the deep beams is described in terms of cracking patterns, load-versus-deflection response, failure mode, and strains in steel reinforcement and concrete. Despite different failure modes, failure loads and corresponding ultimate deflections were similar in all 4 specimens. Yielding of both longitudinal and transverse reinforcement occurred prior to failure. Based on the test results, the shear design procedures contained in the ACI 318-99 Code and Appendix A of the ACI 318-02 Code were evaluated. Both design procedures yielded conservative predictions of the shear strength of the single-span deep beams.

Use of CFRP Overlays to Strengthen Welded Connections under Fatigue Loading

This study evaluates the performance of various methods to prevent and repair fatigue damage in welded connections, a recurring problem that affects a significant number of steel bridges. Experimental tests and analytical simulations were carried out to investigate the fatigue performance of coverplate specimens in which the welded connections were reinforced with carbon-fiber reinforced polymer (CFRP) overlays. Specimens were loaded in three-point bending induced by a cyclic load to evaluate the change in fatigue-crack initiation life of the welded connections caused by the attachment of the CFRP overlays. Test results showed that when bond between the CFRP overlays and the steel was maintained, the reduction in stress demand was sufficient to extend the fatigue life of the welded connections from AASHTO fatigue-design Category E’ in the unreinforced configuration to the infinite fatigue life range. Test results also showed that the fatigue strength of the bond layer was drastically improved by introducing breather-cloth material within the bond layer.

Parametric Analysis of Cross-Frame Layout on Distortion-Induced Fatigue in Skewed Steel Bridges

The effects of skew angle, cross-frame spacing, cross-frame layout, cross-frame stiffness, and load placement on the potential for distortion-induced fatigue damage in steel bridges was investigated by performing a suite of more than 1,000 analysis jobs of high-resolution three-dimensional finite-element models. Susceptibility to fatigue damage was quantified in terms of computed stress demand in the web gap region of the girders. Bridge configurations with three different cross-frame layouts were evaluated, including configurations with cross-frames placed parallel to skew angle (skewed-parallel) and perpendicular to the girder line, both staggered (skewed-staggered) and unstaggered (skewed-unstaggered). Skew angles of configurations evaluated ranged between 0 and 50°, and cross-frame spacing ranged from 2.29 to 9.14 m (7.50 to 30.0 ft). Influence and envelope surfaces were constructed to show the relationship between load placement, location of the maximum web gap stress, and the magnitude of the maximum web gap stress. It was found that maximum web gap stress always occurred when loads were positioned directly above the intersection of a cross-frame and girder web. The parametric study showed that cross-frame stiffness and spacing had a significant effect on the susceptibility to distortion-induced fatigue damage; greater cross-frame stiffness resulted in higher web gap stresses, and increased cross-frame spacing resulted in increased web gap stresses. It was also found that the bridge configuration was key to determining the location of the web gaps where damage is most likely to occur. In skewed-parallel and skewed-unstaggered layouts, maximum web gap stresses were identified in top web gaps, whereas in skewed-staggered configurations, maximum stresses occurred in bottom web gaps. It was found that in configurations with staggered cross-frames, maximum web gap stresses tended to occur in regions of support, where cross-frames are often placed back-to-back along the skewed alignment.

Development of a Technique to Improve Fatigue Lives of Crack-Stop Holes in Steel Bridges

A common technique to prevent the propagation of fatigue cracks in bridge girders is to drill crack-stop holes at crack tips. Stress concentrations at the crack tips are reduced and fatigue life of the bridge is extended. The size of the crack-stop hole needed to prevent further crack growth is determined by using known material properties and relationships developed through experimentation. However, these equations often result in a crack-stop hole diameter larger than can be practically drilled; physical limitations force crack-stop holes to be undersized in the field. To improve effectiveness of undersized holes to that of full-sized holes, a method is needed to strengthen undersized crack-stop holes. This study investigated the potential of a technique to improve the fatigue life of undersized, crack-stop holes. It uses piezoelectric actuators operated at ultrasonic frequencies to convert electrical signals into mechanical work. The technique produced residual compressive stresses of the same order of magnitude as those produced by static cold expansion. A suite of finite element models was created to quantify and characterize the residual stresses surrounding the cold-expanded, undersized, crack-stop holes. Results were compared with analyses in the literature.

Effects of Cross-Frame Placement and Skew on Distortion-Induced Fatigue in Steel Bridges

Because of detailing practices common before the mid-1980s, many bridges are highly susceptible to distortion-induced fatigue. This research explored the influence of cross-frame placement and skew angle in bridges subject to distortion-induced fatigue. Forty high-resolution, three-dimensional finite element analyses of a bridge with multiple cross-frame and skew configurations were performed to examine the relationships between skew angle, cross-frame placement, and stresses on distortion-induced fatigue susceptibility. Bridges with skew angles of 0°, 20°, and 40° and cross-frames spaced at 4.58 m (15 ft) and 9.15 m (30 ft) were investigated. Cross-frame configurations examined included staggered perpendicular to the girder line as well as parallel to the support skew. The analyses found maximum stresses in the web-gap occurred in positive moment regions but not necessarily in regions of highest differential deflection. In configurations with cross-frames placed parallel to the skew angle, maximum stress demand was in the top web-gap but it was in the bottom web-gap region when cross-frames were staggered. Increased spacing between cross-frames correlated with slightly increased maximum web-gap stresses for parallel-to-skew cross-frame arrangements and decreased maximum web-gap stresses for perpendicular-to-girder line cross-frame arrangements. Skew angle had a minimal effect on web-gap stresses in the bridge studied.

Fatigue Enhancement of Welded Details in Steel Bridges Using CFRP Overlay Elements

AbstractCarbon-fiber reinforced polymer (CFRP)-overlay elements were developed with the purpose of enhancing the fatigue performance of welded connections in steel bridge girders. Fatigue tests of seven specimens, including four CFRP-strengthened specimens and three control specimens, were performed to quantify the effect of the CFRP overlays on the fatigue crack initiation lives of the welded connections. Results showed that bonding of CFRP overlays significantly reduced the stress demand on welded connections tested at high stress ranges, leading to a large increase in fatigue crack initiation life. The level of effectiveness of the CFRP-overlay elements in extending the fatigue crack initiation lives of the tested connections was found to be affected primarily by bond strength under cyclic loading; bond strength was found to be dependent on the composition and thickness of the resin layer used to bond the CFRP to the steel. With the AASHTO fatigue design curves as a frame of reference, it was found tha...

Drift-dependent confinement requirements for reinforced concrete columns under cyclic loading

This paper examines the influence of transverse reinforcement and axial load on the drift limit of rectangular columns using test results from 184 specimens subjected to cyclic loading. Columns within the set were selected to have shear span-to-depth ratios of at least equal to 2.5 so that truss action would be the main mechanism of shear resistance and the deformation component related to shear would be small compared with that related to flexure. Expressions relating the limiting drift ratio to the axial load ratio and the amount of confining reinforcement were evaluated. Equations indicating the amount of confining reinforcement required to achieve a given limiting drift ratio for reinforced concrete columns in regions of moderate and high seismicity are proposed.

Use of CFRP Overlays to Repair Fatigue Damage in Steel Plates under Tension Loading

AbstractFiber-reinforced polymer (FRP) overlays have been successfully used in the aerospace industry to repair fatigue damage in aluminum plates. With this success there is potential for use of similar FRP overlays to repair fatigue damage in aging steel bridge structures. This study investigated the effectiveness of repairing fatigue damage in steel plate with adhesively bonded carbon fiber–reinforced polymer (CFRP) overlays. A total of 15 steel plate specimens with preexisting fatigue cracks were repaired with varying thicknesses of CFRP overlays to evaluate the effect of the ratio of axial stiffness of the composite to that of the underlying steel, the axial stiffness ratio (SR), on increased fatigue life and decreased applied stress. The results showed that increasing the axial stiffness ratio from 0 to 0.4 could increase the fatigue life by a factor of 10 for the most extreme conditions, and with an optimal axial stiffness ratio infinite fatigue life may be reached. Fatigue life of the steel specime...