Sergio M. Alcocer

The “Building Code Requirements for Structural Concrete” (“Code”) covers the materials, design, and construction of structural concrete used in buildings and where applicable in nonbuilding structures. The Code also covers the strength evaluation of existing concrete structures. Among the subjects covered are: contract documents; inspection; materials; durability requirements; concrete quality, mixing, and placing; formwork; embedded pipes; construction joints; reinforcement details; analysis and design; strength and serviceability; flexural and axial loads; shear and torsion; development and splices of reinforcement; slab systems; walls; footings; precast concrete; composite flexural members; prestressed concrete; shells and folded plate members; strength evaluation of existing structures; provisions for seismic design; structural plain concrete; strut-and-tie modeling in Appendix A; alternative design provisions in Appendix B; alternative load and strength reduction factors in Appendix C; and anchoring to concrete in Appendix D. The quality and testing of materials used in construction are covered by reference to the appropriate ASTM standard specifications. Welding of reinforcement is covered by reference to the appropriate American Welding Society (AWS) standard. Uses of the Code include adoption by reference in general building codes, and earlier editions have been widely used in this manner. The Code is written in a format that allows such reference without change to its language. Therefore, background details or suggestions for carrying out the requirements or intent of the Code portion cannot be included. The Commentary is provided for this purpose. Some of the considerations of the committee in developing the Code portion are discussed within the Commentary, with emphasis given to the explanation of new or revised provisions. Much of the research data referenced in preparing the Code is cited for the user desiring to study individual questions in greater detail. Other documents that provide suggestions for carrying out the requirements of the Code are also cited.

Two full-scale beam-to-column connections in a precast concrete frame were tested under uni-directional and bi-directional cyclic loading that simulated earthquake-type motions. Variables included the detailing used at the joint to achieve structural continuity of the beam reinforcement, and the type of framing (whether two-dimensional or three-dimensional). The most relevant feature of the connection is that conventional mild steel reinforcing bars or prestressing strands, rather than welding or special bolts, were used to achieve beam continuity. Specimen design followed the strong-column-weak-beam concept. Beam reinforcement was purposely designed and detailed to develop hinges at the joint faces and to impose large inelastic shear force demands into the joint. During specimen fabrication, the joint details enabled ease and speed of construction. As expected, the joint controlled the specimen failure. In general, the performance of both beam-to-column connections was satisfactory. Joint strength was 80 percent of that expected for monolithic reinforced concrete construction. Specimen behavior was ductile due to hoop yielding and bar pullout, while strength was nearly constant up to drifts of 3.5 percent.

In this study, a performance-based model is proposed, capable of simulating seismic behavior of typical confined masonry (CM) walls whose response is governed by shear deformations. This model is developed on the basis of both monotonic and reversed-cyclic experiments assembled in an extensive database, and derived through an iterative linear regression analysis. Owing to the limited data available and inconsistencies in observed behavior in some tests, only specimens with two tie columns, one on either edge of the wall; multiple longitudinal rebar per confining element; no bed joint reinforcement; no openings within the confined panel; and a height-to-length ratio that varies from 0.7 to 1.2, are considered for the purpose of model development. The effect of openings on strength characteristics, the capability of existing models to predict seismic behavior of CM walls, and the limitations of the proposed equations are discussed in detail. The accuracy of the model is also verified for CM walls with different characteristics. The proposed model simulates reasonably well the seismic behavior of CM walls whose properties conform to the assumptions of the model and that correspond to typical CM walls.

Results from an experimental series of seven full‐scale confined masonry walls with height‐to‐length aspect ratios ( H/L ) from 0.3 up to 2.2 are summarized. Results show that neither the level of axial stress nor the aspect ratio had a significant effect on lateral stiffness. Inelastic behavior of the walls, characterized by normalized stiffness degradation with ductility demand, can be estimated with good accuracy with a bilinear function for a ductility demand up to 4.5. A substantial increase in normalized shear strength was observed for walls with decreasing aspect ratio. A correction factor to the nominal cracking strength was deduced based on differences of the flexural deformations for squat and square walls. The factor was then compared to the experimental normalized strength with good agreement. A new expression for inclined cracking shear that can be used for a wide range of wall aspect ratios is proposed.

The extended damage in beam-column connections, particularly during earthquakes, prompted researchers and designers in the 1970's to investigate the behavior of that region, as well as to develop analysis and design criteria. The ACI-ASCE 352 Committee published the first comprehensive technical guideline for the analysis, design and detailing of beam-column joints in 1976. Since then, the report, and its revisions, has been widely used by designers throughout the world, thus leading to better designs or reinforced concrete (RC) frame buildings. Moreover, this document has served as a cornerstone for the development of RC building codes in different countries. The simple, yet conservative, model of joint behavior and the document format are most appealing to the practice. It is the aim of this paper to briefly describe the evolution of ACI-ASCE 352 Committee report on beam-column joints (now referred to connections), and to briefly present main modifications and additions to the most recent revision.