Journal of Structural Engineering

Case studies of the design of an office building employing three-dimensional (3D) eccentrically braced frames (EBFs) as the primary seismic lateral force resisting system are discussed in detail. The floor framing system consists of composite beams supported by long span trusses, which are then supported by eight exposed composite columns. The lateral system is a dual system. The primary lateral system is made of four EBFs supported by the eight composite columns and folded around the four corners of the main building. The secondary lateral system is a moment resisting space frame consisting of the floor trusses and the composite columns. The development of an inelastic two-dimensional analytical model for the 3D EBFs are described. Nonlinear pushover and earthquake response history analyses indicate that the dual structural system possesses substantial reserve strength over the code prescribed minimum lateral loads. The member yielding sequence and the distribution, as well as the extent of the plastic hinge rotations observed from the analyses illustrate that the building is likely to perform satisfactorily under severe seismic events.

This paper provides a summary of typical damages inflicted on steel reinforced concrete (SRC) structures in Japan, during the 1995 Hyogoken-Nanbu earthquake. The paper is based on observations made by the writers during their visits to the damaged areas. SRC structures are a class of composite structures that have been used in Japan for over 30 years. Research on SRC building components dates back to the 1930s. There was a close correlation between the age of the structures and the observed damage. A majority of the damage was inflicted on SRC structures constructed prior to 1970. However, damage to newer SRC structures was also observed. Typical damage was related to (1) large tie spacing in columns; (2) base plate details; (3) vertical discontinuity in building stiffness; and (4) foundation-related failures. Additionally, the use of 90° hooks, even in conjunction with close tie spacing, resulted in inadequate seismic performance.

This paper compares National Earthquake Hazards Reduction Program (NEHRP), Structural Engineers Association of California (SEAOC), ASCE 7, and Uniform Building Code (UBC) seismic design provisions to address the differences in their philosophies and applicabilities. These documents are compared by focusing on issues such as (1) purpose of earthquake codes; (2) type of document and target audience; (3) lateral forces; and (4) analysis provisions. NEHRP and ASCE 7 documents are based on strength design while UBC and SEAOC are based on allowable or working stress design. There are other fundamental differences among these documents such as the required methods of analysis, building importance, detailing requirements, soil amplification factors, drift control and P-delta amplification, and the method of assigning an importance factor. Several tables and graphs are presented to illustrate the similarities and differences among these codes.

An innovative seismic upgrading technique for existing reinforced concrete frame connections constructed prior to the 1970s using corrugated steel jacketing is proposed and evaluated. Six, one-third scale, reinforced concrete beam-to-column connections were tested under quasi-static cyclic loading to study their seismic performance. The investigated test parameters include the amount of joint and column transverse reinforcement, corrugated steel sheet thicknesses, and jacketing of column only or of both column and beam. Test results demonstrated that existing reinforced concrete frame connections upgraded using corrugated steel jackets performed satisfactorily when subjected to high cyclic load levels. The corrugated steel jacket was found to be an effective system of upgrading as it increases the joint shear strength and the energy dissipation capacity. A method for the design of the corrugated steel jacket thickness and depth of corrugation is formulated.

The developments in the last three decades in the area of seismic design of mechanical and electrical equipment, architectural components, as well as other secondary structures and nonstructural components attached to the floors, roof, and walls of buildings are reviewed here. A description is made of what constitutes a secondary structure, the characteristics that make these systems particularly susceptible to the effects of earthquakes, and the parameters that affect their response to earthquakes. The methods that have been proposed and are available to improve and simplify the analysis of this type of structure, the methods that are currently used as reflected by various building codes and seismic provisions, and the experimental studies and field observations carried out to further investigate some of their dynamic properties and response characteristics are also reviewed here. The paper closes with a summary of what research is still needed to advance current efforts to protect these systems against the effects of earthquakes and to develop methods and techniques to achieve this goal in a practical and economical way.

The dissipative capacity of friction-damped bracing systems is evaluated by a statistical characterization of the amplitude and frequency of the slip excursions during a seismic excitation. One-story, friction-damped braced frames are subjected to artificially generated stationary accelerograms, which are compatible with the normalized elastic response spectrum proposed by Eurocode 8. The dynamic response of these frames is analyzed by a step-by-step procedure, which accounts for the variation in the structural parameters, identified by suitably modeling the force-displacement cycle of the dissipative bracing system. Approximate analytical expressions of the aforementioned quantities, characterizing the hysteretic behavior of the frame, are also deduced. These expressions are then utilized to define the range of optimal values of the global slip load leading to a high performance of the devices. The criterion adopted to model the force-displacement cycle of the friction-damped bracing system can be opportunely applied to bracing systems involving different dissipative mechanisms, such that the results obtained can be generalized. Moreover, a criterion of equivalence is proposed, which makes it possible to extend the conclusions of the study to multistory braced frames for which the structural parameters of the equivalent one-story system represent global parameters. Some practical applications pertaining to the case of an actual seismic accelerogram show the validity of the design suggestions proposed.

Two analysis models for high damping rubber bearings are proposed based on the results of shaking table tests of a seismically isolated bridge deck. These analysis models are established using the modified Gauss-Newton system identification method and the fractional derivative Kelvin model based on sinusoidal test results. The tests produced a maximum shear strain in the bearing of approximately 100%. Two existing equivalent linear models specified by the American Association of State Highway and Transportation Officials and the Public Works Research Institute of the Japanese Ministry of Construction are also characterized using sinusoidal test results. The predicted seismic responses of the test structure by the proposed models and the two equivalent linear models are compared with the measured responses. It is concluded that the proposed models can predict the seismic responses of the bearing better than the two equivalent linear models. For practical applications, the fractional derivative Kelvin model is implemented into an iteration procedure adopted by the current design practice. An evaluation of the convergence of iteration and the accuracy of prediction is conducted.

The objective of the paper is to describe the behavior of metal-plate-connected (MPC) tensile and heel joints under seismic and cyclic loads. A proposed sequential phase displacement (SPD) loading standard was also used to determine dynamic characteristics (energy dissipation, damping ratio, and cyclic stiffness) of MPC joints. Strengths and stiffnesses of MPC joints after the seismic and SPD loadings were compared to those properties for a control group of joints tested to failure under a static ramp load. Strength degradation was not observed in tensile and heel joints as a result of the seismic loads. Stiffness degradation was observed in the heel joint as a result of the large artificial earthquake loads and in both tensile and heel joints as a result of the SPD loading. Dynamic properties from the SPD loading depended on the magnitude of displacement. The damping ratio and energy dissipation increased as the SPD loading progressed, whereas the cyclic stiffness decreased. Cyclic loading also showed a significant effect on the strength of MPC joints depending on the amplitude of the cycles.

Stressed-skin panels (SSP) of mixed construction were made of various combinations of wood-based materials or lightweight concrete plates as the compression flange and a thin steel-sheet tension flange. An approximate method was developed for computing the stiffness of a SSP with flanges attached with various degrees of rigidity to spaced timber webs loaded in bending. Using this method, SSP deflection was calculated with a magnification factor, which reflected different slip moduli for joints between the webs and two flanges and by twice utilizing a two-layer model. The deflection predictions using this simple procedure compared well with the results of experiments performed on all panel types studied. However, when the load level exceeded approximately 60% of SSP capacity (which is well above the expected stress level in service), the predictions became less accurate. Finally, it was found that thin steel sheet tension flanges improve the total stiffness of the wood-based SSP.

This paper presents a discussion of salient issues surrounding the modeling and performance of bolted connections in wood construction. To understand the complex behavior of bolted joints under load, a number of key issues related to connection geometry, material, and mechanics need to be understood. Issues addressed in this paper include the design philosophy of bolted joints (allowable stress and reliability-based design), the influence of connection geometry on behavior under load, and a discussion of previous models that have been used to predict connection performance. Discussions of the key models used to predict connection behavior, including the European yield model, which currently serves as a basis for allowable connection load in U.S. codes, and various failure criteria are presented. Of particular interest is the discussion of the strengths and weaknesses of the two-dimensional (2D) models that have been used historically to quantify connection behavior. These are seen relative to developments in three-dimensional (3D) modeling of bolted connections. The contributions of modeling pin/wood contact surfaces to connection behavior prediction are also considered.

Three-dimensional (3D) constitutive models for wood were developed and evaluated for use in a 3D numerical model of a bolted wood connection. The connection model applies to parallel-to-grain loading of wood. Nonlinear parallel-to-grain compression of wood and degradation of shear stiffness are described using a trilinear stress-strain relationship. Elastic parameters were determined that best fit numerically predicted load-displacement (P-Δ) curves to those obtained from experiments on bolted connections. The connection model also accounted for an elastic–perfectly plastic steel pin, oversized hole, and a changing contact surface at the pin-hole interface. The numerically obtained P-Δ curves were generally stiffer than the experimental curves but displayed important characteristics found in the experimentally obtained curves. Effects of material property assumptions and different forms of the trilinear curves were also evaluated.

A longitudinal shear testing program was carried out on full-size, Mexican pine lumber. The samples for the tests were taken from five sawmills located in three different states of Mexico: the two most important, regarding production, and the one closest to Mexico City, the largest market in the country. The shear testing program was the last part of the “Stress Grading of Mexican Pine Lumber” project. The results presented here should be considered in the next revision of the “Structural Design Code of Wood Structures” for Mexico City. Design values for longitudinal shear are derived. Two adjustment factors are proposed: one is the moisture content factor (K_h) and the other is the size effect factor (K_p).

Recent results from full-scale static racking tests and small-scale lateral shear tests on plywood, oriented strand board (OSB), gypsum wallboard (GWB), and FiberBond wallboard (FB) attached to light gauge steel studs are presented and discussed in this paper. The objectives of the tests were to investigate the performance of sheathed light gauge steel framed shear walls and determine whether simple static lateral shear values for the panel connection can provide a useful correlation with full-scale test values. The full-scale tests were conducted in accordance with the basic test criteria defined in ASTM E 72-80. A procedure similar to that described in ASTM D 1761-88 was used for the small-scale tests. Panels used in the tests included 11.9 mm APA rated four-ply plywood sheathing, 11.1 mm APA rated OSB sheathing, 12.7 mm gypsum wallboard (ASTM C 36), and 12.7 mm FiberBond wallboard. Results obtained from tests showed that failure of the walls resulted from rotation (tilting) of the fasteners about the plane of the stud flange followed by either the head of the screw pulling through the panel or the screw breaking the edge of the panel. In the small-scale tests, failure resulted from the fastener breaking the edge of the panel. Normalized lateral shear connection resistances were found to be relatively close to the corresponding normalized racking shear values for the full-scale test. Thus, it appears that small-scale connection tests may be used as a good predictor of the behavior of full-scale walls.

The purpose of this study is to investigate the behavior of prestressed concrete members containing unbonded tendons. First, a time-dependent nonlinear constitutive law for concrete was proposed in such a way that a solution can transit continuously in the displacement field. Next, the hybrid-type element method was derived to improve the computational capability of stresses and strains, especially for the unbonded tendon. Then, a computational method for the consideration of unbonded tendons was developed consistently with the analytical method of structure. Along with these, a computer program time-dependent analysis for prestressed concrete structures (TAPS) was developed and three numerical examples was solved to verify its capability. In the companion paper, experimental results in the literature were analyzed to investigate the load-deflection behavior of unbonded members and the stress variation of unbonded tendon at flexural failure.

In a companion paper, the program time-dependent analysis for prestressed concrete structures (TAPS) was developed for the analysis of prestressed concrete members with unbonded tendons. In this paper the inelastic behavior of unbonded members under various loads is studied. With the program, experimental data in the literature were investigated to examine the load-deflection response and the tendon stress at flexural failure. A total of 30 tests on simply supported and continuous members with unbonded tendons were analyzed with the program. The load-deflection responses were compared favorably with experimental data. The stress changes in unbonded tendon were compared with the stresses computed by the American Concrete Institute (ACI) code, Naaman and Alkahairi's equation, and TAPS. The analytical study showed that the tendon stress at flexural failure was affected significantly by the bonded reinforcement, the length of plastic hinging zone.

Robert Maillart's dimensioning procedure for orthogonally reinforced flat slabs is reviewed and compared with methods of elastic plate theory and limit analysis. It is shown that compared to an elastic analysis, Maillart considerably underestimated the flexural moments acting in flat slabs. However, based on comparisons with limit analysis procedures, Maillart's designs are characterized by reasonable safety margins. It is demonstrated that the efficiency of the reinforcement according to Maillart's design approach agrees well with that of current design methods. While Maillart's work was far ahead of his time it appears to have had little impact beyond his own numerous designs. Substantial spreading of flat slab construction in Europe occurred only after design methods based on the theory of elastic plates had been developed in the early 1920s. As a by-product of the present investigation, Lewe's elastic analysis of an infinitely large flat slab subjected to alternating strip loading has been corrected.