Harry G. Harris

EARTHQUAKE SIMULATION TESTING OF SMALL-SCALE REINFORCED CONCRETE STRUCTURES

A brief summary of techniques used in earthquake simulation testing of small-scale concrete structures is presented. Actual prototype concrete structures tend to be very heavy, and even small-scale replicas of these present weight problems for many of the existing earthquake-simulator test facilities. Nonlinear, ultimate strength models need to be employed in this type of shaking table investigation. Included is a discussion of similitude, model materials, distortion of mass density scale, and choice of scale factor. A case study of a 7-story 1:5 scale, concrete wall-frame building tested at the University of California, Berkeley, and a case study of several 5-story, 1:32-scale, isolated precast shearwalls tested at Drexel University are discussed. Knowledge gained from studies such as these is important in understanding the behavior of structures under earthquake loading and will help facilitate the development of earthquake-resistant design.

FLEXURAL BEHAVIOR OF JOINT REINFORCED BLOCK MASONRY WALLS

This paper presents an experimental study of the behavior of horizontally spanning joint reinforced block masonry walls under out-of-plane monotonic lateral loading. Five full-scale wall panels were tested to determine the effect of amount and type of horizontal steel and bond pattern (running versus stack bond) on wall behavior including cracking moment, load deflection relationships, and flexural strength. Correlation between flexural strength test results and the UBC-88 code strength design method is presented. The results show that the shape of the load deflection curve was a function of the spacing and type of reinforcement. Details of the results are presented and discussed. It is concluded that as the UBC strength design method gives a reasonable estimate of wall flexural strength, a method based on strain compatibility would provide more accurate results.

Reinforcement For Small Scale Direct Models of Concrete Structures

THE PROBLEM OF PROVIDING SUITABLE REINFORCEMENT IN SMALL SCALE DIRECT MODELS OF REINFORCED CONCRETE STRUCTURES IS EXAMINED IN DETAIL. MAXIMUM ATTENTION IS GIVEN TO BEHAVIOR IN BOND OF SEVERAL DIFFERENT TYPES OF REINFORCING WIRE. BASIC STRENGTH PROPERTIES OF THE WIRES ARE ALSO PRESENTED, ALONG WITH RECOMMENDATIONS ON ANNEALING PROCESSES REQUIRED IN PRODUCING REINFORCEMENT OF PROPER STRENGTH. THE STUDY IS RESTRICTED TO WIRE SIZES NOT EXCEEDING ABOUT 1/6 IN. DIAMETER. SURFACE DEFORMATIONS ON MODEL WIRES ARE EXAMINED IN RELATION TO THE ACTUAL SIZES AND PATTERNS OF DEFORMATION ON MODERN DEFORMED PROTOTYPE BARS. COMMERCIALLY AVAILABLE THREADED WIRES AND DEFORMED WIRES WERE INVESTIGATED, AS WELL AS A SPECIALLY DEFORMED WIRE PRODUCED IN THE CORNELL STRUCTURAL MODELS LABORATORY. BOND PULLOUT TESTS WERE MADE WITH EACH OF THE VARIOUS DEFORMED WIRES AND WITH PLAIN WIRES, USING SCALED DOWN CYLINDRICAL CONCRETE SPECIMENS OF 1 IN. DIAMETER. VARIABLES INCLUDED WIRE DIAMETER, EMBEDMENT LENGTH RATIO L/D, AND TYPE OF MODEL CONCRETE (BOTH CEMENT AND GYPSUM MORTARS). TEST RESULTS ARE COMPARED WITH SIMILAR TESTS ON PROTOTYPE DEFORMED BARS. IT IS CONCLUDED THAT PLAIN WIRES DO NOT ADEQUATELY MODEL THE BOND CHARACTERISTICS OF PROTOTYPE DEFORMED BARS, BUT THAT ULTIMATE BOND STRENGTHS MAY BE MODELED SUCCESSFULLY WITH PROPERLY DEFORMED MODEL WIRES. TENSILE CRACKING STUDIES WERE MADE TO INVESTIGATE CRACKING SIMILITUDE. WIRES EMBEDDED IN RECTANGULAR MODEL CONCRETE SECTIONS (MODELED AFTER PROTOTYPE TESTS BY BROMS) OF DIFFERENT SCALES WERE SUBJECTED TO TENSION; THE RESULTING CRACK PATTERNS WERE COMPARED TO PROTOTYPE RESULTS. WHEN APPROPRIATELY DEFORMED WIRES WERE USED, THE NUMBER OF PRIMARY CRACKS AT SIMILIAR STRESS LEVELS COMPARED CLOSELY WITH THE PROTOTYPE RESULTS. SPECIMENS CONTAINING PLAIN, UNDEFORMED WIRES DEVELOPED ONLY A SMALL PERCENTAGE OF THE TOTAL NUMBER OF CRACKS. DUPLICATE SPECIMENS OF EACH TEST GAVE CLOSE RESULTS, INDICATING ADEQUATE REPRODUCIBILITY OF THE MODEL TESTS. /ACI/

Seismic Evaluation of an Elevated Highway Bridge in a Low Seismic Region - a Case Study

This paper presents the results of the seismic evaluation of an elevated seven-span bridge with tall piers in western Pennsylvania. The bridge was modeled using the SEISAB software, and the analysis used modal superposition method. Various modeling strategies related to piers, abutments, expansion joints, fixed joints, rocker bearings, and hanger supports were studied. Several modeling options were made to capture different behavior responses under seismic loading conditions. The force and displacement demands are compared, and an assessment is made with respect to the potential for damage based on the analysis results. The result of the study shows that for the level of earthquakes expected in the region, columns will not be overstressed. Furthermore, the analysis results show that displacements of the superstructure should not be of concern in light of the fact that there is sufficient bearing seat width and that concrete pedestals have been added in front of the bearing supports to presumably prevent the walking off of the bearing from the support. The study concludes that considering the low level of earthquakes expected in PA, the potential for collapse of the superstructure due to bearing support failure is negligible. The paper contributes to better understanding of the behavior of tall and elevated highway bridges in low seismic regions. The results of the study reinforce the view that decisions on seismic retrofit of such bridges in low seismic regions should not be based on column tie spacing.

Use of Structural Models as an Alternative to Full-Scale Testing

A brief review is given of the requirements to be met by small-scale direct models in duplicating the behavior of actual structures up to ultimate failure. It is found that the requirements on similitude, model materials,fabrication, and testing techniques are more restrictive in model studies where nonlinear structural behavior is the primary goal. The paper discusses current methods of structural modeling for the most common structural forms, materials of construction and loading. Examples of model studies of a variety of structures, drawn mainly from practical applications of the modeling technique are given. In all the examples chosen, the main objective has been the duplication of the inelastic structural behavior of the anticipated prototype structure under both static or dynamic loads.

Nonlinear analysis techniques of block masonry walls in nuclear power plants

Abstract Concrete masonry walls have been used extensively in nuclear power plants as non-load bearing partitions serving as pipe supports, fire walls, radiation shielding barriers, and similar heavy construction separations. When subjected to earthquake loads, these walls should maintain their structural integrity. However, some of the walls do not meet design requirements based on working stress allowables. Consequently, utilities have used non-linear analysis techniques, such as the arching theory and the energy balance technique, to qualify such walls. This paper presents a critical review of the applicability of non-linear analysis techniques for both unreinforced and reinforced block masonry walls under seismic loading. These techniques are critically assessed in light of the performance of walls from limited available test data. It is concluded that additional test data are needed to justify the use of nonlinear analysis techniques to qualify block walls in nuclear power plants.

Nonlinear Modeling of Precast Concrete Large Panel Buildings Under Simulated Progressive Collapse Conditions

Precast concrete large panel (L.P.) building systems form the largest single type of industrialized building construction used in multi-story residential structures currently built in the United States. Large panel reinforced and/or prestressed concrete structures are bearing wall buildings constructed of individual wall and floor elements arranged in a box type configuration. Under normal gravity and lateral loads, L.P. buildings are stable structures that exhibit a very high lateral stiffness. A stability problem can arise in an improperly detailed L.P. building when a portion of the structure is subjected to an abnormal load such as a gas explosion or vehicle impact.