M. J. Nigel Priestley - US grants

Masonry construction comprises a large portion of building construction in the U.S. and the world. Reinforced masonry construction use is increasing in moderate to higher seismic zones because of its apparent features of economy, fire safety, architectural flexibility and ease of construction. The present state of masonry structural analysis and design, and materials and construction technologies does not enable an accurate prediction of building behavior under lateral loads such as seismic loads. In the U.S., masonry buildings are designed and built with methods, codes and standards that rely upon a mixture of working stress methods, empirical rules, and questionable methods for determining allowable stress values. Masonry is also a complex building material because of the large number of design and construction variables which influence the final product configuration and its response under seismic loads. In order to describe the seismic response of masonry buildings it is necessary to develop the fundamental knowledge base to determine basic design methodologies consistent with safety and economic requirements. This research project is a theoretical and experimental investigation of the seismic performance of flanged masonry shear walls. The theoretical studies develop predictive models for effective flange width under lateral loading and also develop load-displacement component models for lateral hysteretic response that incorporates the separate displacement components resulting from flexure, shear and base-slip deformation. Particular emphasis is placed on the asymmetrical strength, stiffness, and ductility characteristics of T-section walls loaded parallel to their web. The experimental studies involve static cyclic load testing of T-section masonry walls and dynamic shake-table testing of T-section and rectangular section walls. The tests are on full-scale elements and are used to verify and calibrate the models developed during theoretical studies. This project is part of the U.S.-Japan Coordinated Program for Masonry Building Research and the Technical Coordinating Committee for Masonry Research (TCCMAR) Program.

Damage to the freeway bridges in the Whittier Narrows earthquake of October 1, 1987 was one of the most significant aspects of damage to engineered structures designed for seismic lateral loads. Of particular importance was the performance of the I-605/I-5 separator, which was extensively damaged during the earthquake and came perilously close to collapse at a time when freeway traffic was at its heaviest and loss of life would have been extensive. The research project is directed to a study of the performance of freeway bridges in the Whittier Narrows earthquake. The research involves five stages: observed damage assessment, component strength and deformation analysis, dynamic analysis of selected bridge structures, recommendations on assessment and evaluation and prioritization for retrofitting. The intention of the research is to obtain maximum benefit from the lessons emphasized by bridge damage in the earthquake in the form of improved understanding of the vulnerability of existing bridge structures to seismic damage, calibration and assessment of analytical techniques for analysis of seismic response of bridge structures, and in the development and assessment of retrofit techniques to reduce the seismic risk of freeway bridges.

This research project supports the initiation stage of the fourth phase of the UJNR Panel on Wind and Seismic Effects Coordinated Research Program, to be on the topic of precast seismic resistant structural systems. The initial stage of this project establishes an administrative structure, sets the aims and limits to the scope of the project, explores cooperative opportunities with the Japanese counterpart, solicits industry support, assembles a group of researchers to form the core of the research effort, and through collaborative effort on their part, prepares a detailed research plan for the fourth phase of the UJNR project. This will then be the program planning document used by NSF in the conduct of this international coordinated earthquake engineering research project.

Within the framework of the joint U.S.-Japan masonry research program, the specific objective of the U.S. program is to develop an experimentally verified design and analysis methodology that will ensure satisfactory performance of reinforced masonry buildings under a wide range of seismic loadings. In particular, under severe earthquake loadings such buildings must exhibit ductile behavior. A key aspect of the philosophy adopted by the U.S. program is to support the design and analysis development by an increasingly complex set of experiments culminating with the study of a five-story full-scale masonry building. This experiment is essential to achieve the objectives of the program in that it will provide the final validation of the analytical and computational models developed, and thus will form the basis for the design recommendations to be made at the culmination of the overall project. This research project is a full-scale building test conducted at the Charles Lee Powell Structural Systems Laboratory at the San Diego campus of the University of California. The experiment is performed using a reaction wall concept, in which the building is subjected to generated displacement histories at the floor levels via hydraulic actuators in a manner that simulates the displacements during an actual seismic event.

This project establishes the coordination base for the U.S. precast concrete research projects. It will integrate the results of the research into readily usable forms and: * organize major coordination meetings of all principle investigators at six month intervals, * coordinate activities between U.S. and Japan precast concrete research activities through annual joint meetings, * provide coordination with other precast concrete programs on-going elsewhere, * facilitate transfer of technology to industry and the design profession. This project will provide an effective mechanism for integration of the four research projects into a coordinated research effort.

Rehabilitation and strengthening of bridge structures have become a major focal point of the Nation's aging bridge inventory. To mitigate the staggering rehabilitation problem the Bush Administration is on record "...to be committed to develop a strong transportation research and technology program." The workshop will address a vital component of the national transportation research program the nation's bridge inventory and will associated ongoing research efforts. The workshop has three principal objectives, namely (1) to identify the state-of-the-art in bridge design and retrofit research, (2) to develop means of transferring research results to implementable technology and (3) to establish bridge research directions and priorities in support of the nation's bridge infrastructure for the 21st century. The workshop is the third in a series of NSF supported Bridge Research in Progress Workshop and is envisioned to be held in San Diego, California in Fall of 1992.

Precast concrete frames using beam elements connected to multi-story column elements with post-tensioned prestressing tendons has been identified as an economically viable method of construction for tall buildings. Recent research has indicated that beam-column joint subassemblages using fully grouted tendons developed ductility comparable to monolithic reinforced concrete subassemblages designed to current specifications. But the tendons often suffer excessive stiffness degradation at low displacements after moderate ductility levels had been chieved. This was caused by a reduction of effective prestress clamping force through the column, resulting from inelastic strain of the prestressing tendon at the critical section. This project conducts a pilot study to experimentally verify a new concept for connecting precast seismic frames using unbonded prestressing tendons. The tendons will connect precast beam and column sections which allows a nonlinear elastic response and achieves a considerable displacement capacity. This capacity is free from problems associated with permanent deformation, thus enable the joint shear capacity to be enhanced without the need for extensive joint shear reinforcement. Two large scale test units representing an external and an internal connections respectively will be constructed and tested under cyclic lateral deformations using the existing pseudo-dynamic testing facility at University of California, San Diego. Conservative transverse reinforcement details will be chosen and heavily strain gauged. It is expected that recommendations for reduced reinforcement will be made and verification of the concept will be achieved from the experimental research. This project is supported under the provision of Small Grants for Exploratory Research (SGER) program.

9307840 Priestley This project carries out studies for the development of an innovative prestressed reinforced concrete system utilizing precast beams connected to columns by unbonded prestressing tendons continuous over the length of the multi bay frame. The tendons provide continuity and moment resistance to the beams and the tendons remain elastic when flexural cracking develops during seismic response. The major tasks are (l) testings of large scale assemblages, (2) modeling of hysterestic characteristics, (3) time history analyses of multistory frames, and (4) design details development. Considerable advantages in terms of increased frame ductility, simplified joint design, etc. might be achieved through implementation of this innovative PRESSS system concept. ***

9307822 Priestley This project describes the administration base for continued coordination of the U.S. PRESSS project and is a direct extension of an existing coordination project. The project will provide: (l) Coordination of U.S. PRESSS activities, including organization of major coordination meetings of U.S. PRESSS researchers at six month intervals. (2) Coordination between U.S. and Japanese PRESSS activities, including the organization of an annual U.S./Japan coordination meeting. (3) Coordination between PRESSS and related research activities at NIST, ATLSS, and overseas. (4) Coordination between PRESSS and the funding agencies, including NSF, PCI and PCMAC. (5) Technology transfer of PRESSS results to Industry and the design profession in the form of technical reports and journal papers, and special purpose seminars. ***

The first U.S. 5-story full-scale research building which was tested at UCSD under simulated seismic loads to 1-1/2 to two times the seismic design and deformation levels, provides in its damaged state a unique opportunity to develop and experimentally validate new repair technologies. The proposed repair measures consist of epoxy injection, advanced composite wall and floor overlays as well as ceramic foam applications in the hollow core plank floors, with particular emphasis on materials and technologies originally developed and applied in the defense industry to show their potential for application in the civil sector. It is proposed to use loading sequences in the retest which correspond closely to the original seismic load test, in order to get a direct experimental seismic behavior comparison for the verification of the effectiveness of the proposed repair measures. The test results will provide important information about the repairability of damaged reinforced masonry structures and about the expected behavior of repaired structures under future seismic loads.

This project covers the construction and testing of a large scale five-story precast superassemblage under simulated seismic loading. The purpose of the project is to provide a realistic vehicle for verifying structural concepts, design methodology and analytical procedures developed in NSF research initiative `precast and prestresses seismic structural systems` (PRESSS) Phases 1 and 11, and to evaluate the seismic performance of precast designs in terms of reduced damage and residual deformation compared with conventionally reinforced buildings. The project forms the key element of PRESSS Phase III, in accordance with the original PRESSS master plan. The structure will consist of five stories, with a two-bay by two-bay plan. In one direction the lateral bracing will be provided by precast walls, and in the other direction, by precast frames, enabling different structural systems to be tested in orthogonal directions. Different precast flooring systems will be adopted at different levels to investigate diaphragm action and frame-floor connection details. Design will be in accordance with direct-displacement seismic design procedures developed as part of the earlier PRESSS phases. Testing will primarily be under a multi-degree-of-freedom pseudo-dynamic testing procedure developed earlier for a five-story masonry building. Sequential time-histories chosen to exercise the building to a series of limit states including (1) first-cracking, (2) first yield, (3) serviceability limit, (4) damage control, and (5) incipient collapse, will be applied to the structure. Results from the experiment will be used to finalize design recommendations from the PRESSS project. The five-story superassemblage test has extremely strong industry support, with more than 60% of the necessary cost being provided by the precast industry.