International Concrete Abstracts Portal

In virtually all areas of structural engineering, including the increasingly well-known area of structural reliability assessment, it is commonly assumed that failures will occur suddenly and instantaneously in given failure modes. This assumption affords a valuable simplification of complex real-world problems. However, many failure modes do not obey this assumption, including most serviceability failure modes, strength failure modes of ductile component and/or redundant systems, and failure modes based on cumulative damage. For these cases, a formulation is required with which the transition from complete survival to complete failure can be modeled as being gradual and continuous, and comprised of partial failure levels. This paper proposes such a formulation along with corresponding methodologies for structural reliability assessment and reliability-based design. Various statistical and entropy-based measures which can be used to help characterize the results of the structural reliability assessment are also suggested. Application of the proposed structural reliability assessment and reliability-based design methodologies is illustrated with an example problem involving deflection failure of a reinforced concrete beam. Some potential applications of the proposed methodologies include probabilistic design and code calibration for failure modes modeled as having gradual and continuous failure transitions.

Purpose is to present a lesson learned from the findings of the Governor Thomas Johnson Memorial Bridge, Maryland. The bridge has an overall length of 7205 ft, with 59 spans. Thirty-eight piers are made of concrete hammerhead-type pier caps with different height and cap sizes. The cracks observed on the deep water piers initiated the evaluation of these hammerhead-type pier caps. The structural integrity was questioned and several analysis procedures were taken on this case. Extensive computer analyses, including nonlinear finite element analyses were conducted. This paper also intends to depict the implementation of the Code, design methodology, and calculation procedures concerning this type of pier for engineering practices. Finally, the remedial strengthening method using the post-tensioning system is presented.

This paper presents the evaluation of seismic performance of a special moment-resisting (SMR) frame building and an intermediate moment-resisting (IMR) frame building designed in accordance with the NEHRP provisions and ACI Code 318-83. The annual limit-state probabilities for both SMR and IMR frames are determined by integrating the seismic hazard curve and structural fragility curve. From the comparison between the calculated annual limit-state probability and the specified acceptable risk levels, the seismic performance of a structure can be evaluated. In the NEHRP provision, if reinforced concrete frames are used to resist earthquake forces, the SMR frame is required for buildings belonging to higher seismic performance categories such as Categories D and E. Even though the SMR frame has a higher ductility than the IMR frame, the SMR frame is only designed for 50 percent of the strength required for the IMR frame. As demonstrated in this study, the IMR frame may perform better than the SMR frame in the event of an earthquake. Thus, the concept employed in the NEHRP provisions to protect high-risk and essential buildings needs careful reexamination.

SP-133 Design for serviceability and safety is central to the work of structural engineers, code-writing bodies and the users. The current era of high strength materials, exotic additives and limit states of design has necessitated better control of constructed facilities in their short and long-term behavior at service load and at ultimate load. This Special Publication concentrates on topics that give the design engineer and contractor an insight into how to avoid practices that could affect the integrity or long-term performance of structural elements and systems. The text is outgrowth of a national symposium of the American Concrete Institute co-sponsored by ACI Committees 348 and 435, and covers topics ranging from crack-control in reinforced and prestressed concrete, safety provisions in design codes and practical deflection computations to limit state design principles and seismic performance of frame structures. Several papers that could not be presented due to time limitations are included. The papers dealing with serviceability, highlight requirements of the ACI Codes and Reports in addition to relevant state of the art developments. The paper covering safety deal with issues ranging from philosophical discussions of treatment of safety in codes to project case studies. Overlap is expected since serviceability and safety are indivisible. All the papers presented in this publication were reviewed by recognized xperts in accordance with the ACI review procedures. It is hoped that designer, constructors and codifying bodies will be able to draw on the material presented in improving the safety and long-term cracking and deflection behavior of concrete constructed facilities.

Studies are limited on the early age performance of high-strength cold weather concretes and their shear strength interaction in cold weather. This paper presents shear transfer strength characteristics between regular high-strength concrete and (i) methyl methacrylate-based polymer concrete and (ii) magnesium phosphate based concrete in subfreezing temperatures. Analytical expressions were developed based on shear transfer hypothesis and verified by experimental results. The experimental study included tests on cylinders and L-shaped push off specimens to determine the early age shear interlock and shear frictional resistance between high-strength regular portland cement concrete and cold weather high-strength concretes as is experienced in rehabilitation of bridge decks and other infrastructure systems. Studies indicated that at early age of 24 hours, shear transfer strength of 1400 psi can be obtained with the use of appropriate material and shear reinforcement. The study also indicated the ACI 318-89 code limits on the shear-friction strength are too conservative even at early ages for high-strength cold weather concretes.