Thomas A. Sabol

Reinforcing of steel moment connections with cover plates: Benefits and limitations

Steel moment connections reinforced with cover plates have received considerable attention in the US since the Northridge earthquake, both in laboratory testing and in new steel moment frame construction. This paper presents experimental data on 12 large scale connection test specimens reinforced with cover plates. Ten of the 12 test specimens showed excellent performance, developing large plastic rotations under cyclic load. Two test specimens failed, however, indicating that cover plated connections are not fool-proof. This type of connection has limitations that must be considered in design and construction. The paper provides a critical assessment of cover plated connections, identifying potential benefits as well as concerns and limitations. Design implications of the experimental data are discussed.

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.

Estimation of seismic-induced demands on column splices with a neural network model

The current seismic design specification (AISC 341-05) requires that column splices in moment frames, when not made using complete joint penetration (CJP) welds, be designed to develop the flexural strength of the smaller connected column and the shear demand associated with flexural hinging at the top and bottom of a spliced column at a given story. AISC 341-05 assumes that the beam-to-column connection would reach its critical limit state before the column splice does. Estimating seismic demands on column splices involves both ground motion and structural parameters, i.e., it is a high order nonlinear and complex problem. This study presents a Neural Network (NN) model to estimate the seismic demands on column splices in low-, medium-, and high-rise steel moment frames. Nine input parameters and 6 output parameters were used to construct the NN model. The effect of each input parameter on the output parameters (seismic demands on column splices and frame) was investigated through a sensitivity analysis based on the NN model.

Calibration of strength reduction factors for concrete masonry

Abstract Despite the variation in structural reliability which results from a combination of the current non-probabilistically derived load and strength reduction factors. the number of structural failures involving concrete members is quite small. This suggests that it would be reasonable to identify the mean values of reliability for the different limit states according to present code formulations and to calibrate the new strength reduction factors to match these mean levels of reliability. Such work has been done in concrete and a set of revised strength reduction factors has been developed. In this study we will develop a set of strength reduction factors which are calibrated to the strength reduction factors given elsewhere. This set of strength reduction factors is developed by considering the relative uncertainty in failure modes and loading states between the two materials, concrete and concrete masonry, which are involved in the calibration.

Optimization of ductility in concrete ductile frames

Abstract An investigation of the parameters affecting the optimization of curvature ductility in a reinforced concrete frame sub-assembly subjected to seismic loads is presented using the feasible directions method. Four design variables are used: width of beam cross section, effective depth of cross-section, area of tension steel, and compression reinforcing. Two other variables, concrete compressive strength and yield strength of reinforcement, are treated as preassigned parameters because these quantities are usually taken as integer values in structural design. Curvature ductility is maximized for a given demand moment when one uses: the lowest yield strength steel and the highest concrete strength available; equal amounts of tension and compression reinforcement; the largest cross-section permitted by the design constraints; and sufficient reinforcement to just satisfy the demand moment constraint.