Journal of Structural Engineering

An alternative and efficient procedure to estimate the maximum inelastic roof displacement and the maximum inelastic interstory drift ratio along the height of regular multistory steel MRF subjected to pulselike ground motions is proposed. The method and the normalized response quantities emerge from formal dimensional analysis which makes use of the distinct time scale and length scale that characterize the most energetic component of the ground shaking. Such time and length scales emerge naturally from the distinguishable pulses which dominate a wide class of strong earthquake records and can be formally extracted with validated mathematical models published in literature. The proposed method is liberated from the maximum displacement of the elastic single-degree-of-freedom structure since the self-similar master curve which results from dimensional analysis involves solely the shear strength and yield roof displacement of the inelastic multidegree-of-freedom system in association with the duration and acceleration amplitude of the dominant pulse. The estimated inelastic response quantities are in superior agreement with the results from nonlinear time-history analysis than any inelastic response estimation published previously.

This paper attempts to provide insight into the sensitivity of the collapse capacity of moment-resisting frame and shear wall structures to variation in basic structural parameters, and the choice of an appropriate ground motion intensity measure, based on probabilistic estimation of the collapse capacity of a structural system. The effects of fundamental period and base shear strength and of deformation and deterioration properties of structural components on the collapse capacity of frame and wall structures are quantified. It is shown that the collapse potential of moment-resisting frames is highly sensitive to the ratio of column to beam strength; increasing this parameter from 1.2 to 2.4 will increase the median of collapse capacity by up to 90%. Using a scalar ground motion intensity measure for estimating the collapse capacity can lead to underestimation of median collapse capacity by up to 50%, compared to using a vector-valued intensity measure. The provided information can be used to assist in the selection of a suitable structural system and associated parameters in design for collapse safety. Closed-form solutions are formulated using a database of collapse fragility curves developed for the sensitivity study. Application of these closed-form solutions for design decision making is illustrated through a comprehensive example.

To investigate the mechanical behavior of bidirectional spring units used as isolators in a kind of isolated floor system, three types of characterization tests were conducted—from spring components alone to the complete spring unit in its implemented configuration. The test results show that the behavior of the springs and spring units is stable when subjected to cyclic repeated motions, and is not sensitive to the velocity of motion. The hysteretic behavior of the spring units was found to be unconventional, with bilinear and different ascending (loading) and descending (unloading) branches. Based on the experimental behavior, a physical model was developed to replicate the unique behavior of such bidirectional spring units. Good agreement was found from the comparison between the results from the physical model and the corresponding tests. Finally, a sensitivity study, with respect to the model’s four primary defining parameters, shows that this physical model is more sensitive to the sliding friction coefficient between the spring cable and the bushing in the spring unit than to the other three parameters.

A cyclic testing of nine full-scale beam-to-column moment connection subassemblies was carried out to support the development of design provisions for a lateral load-resisting system in the AISI S110: Standard for Seismic Design of Cold-Formed Steel Structural Systems—Special Bolted Moment Frames. This type of one-story framing system features C-section beams connected to hollow structural section columns by bearing-type high-strength bolts and is commonly used in industrial platform construction. The test results showed that these specimens had an interstory drift capacity significantly larger than 0.04 rad. The cyclic behavior was characterized by a linear response, a slip range, and a significant hardening response due to bearing at bolt holes. The conventional strong column-weak beam design philosophy is not appropriate for this system. The inelastic action through the bolt slip and bearing in the connection is a ductile yielding mechanism. Beams and columns should be protected to remain elastic by the capacity design principles. Based on the concept of the instantaneous center of rotation of an eccentrically loaded bolt group, a model that can properly simulate the cyclic behavior of the bolted moment connection is presented.

The American Iron and Steel Institute (AISI) recently issued a standard on the seismic design of cold-formed steel special bolted moment frames (SBMF). It is expected that ductility is provided through bolt slippage and bearing in the moment connection region; both the beams and columns are to be designed based on the capacity design principles. This paper provides background information for the proposed seismic performance factors. Based on cyclic testing results, a value of 3.5 was proposed for the response modification coefficient, $R$ . A statistical evaluation through nonlinear time-history analysis, which considered the unique structural characteristics of this framing system, showed that the Newmark-Hall ductility reduction rule is conservative. Based on the analysis results, a revised rule was proposed, which resulted in a deflection amplification factor, $C_d$ , of $R/1.2\left(\approx 3.0\right)$ . A design procedure in the AISI seismic standard allows the designer to directly calculate the maximum seismic force in the moment connection at the design story drift level, thereby an empirical system overstrength factor, ${\Omega }_0$ , is unnecessary for the design of SBMFs.

Flooring systems containing steel-concrete composite beams are common in steel frame structures and it is widely recognized that their behavior under fire loading is profoundly different to that of simply supported composite beams under fire loading. This difference in behavior is due to the presence of restraints provided by cooler members in a compartment fire in a composite frame structure and there is extensive evidence from fire tests that composite beams with unprotected steel components in steel frames perform much better than simply supported composite beams with unprotected steel components. In order to model the structural response of a composite beam restrained in this way at elevated temperature, recourse is needed to a geometric nonlinear formulation, since the transverse beam deflections are large and interact with the substantial axial compressive force in the member at the early stages of the fire. This paper presents such a formulation, which incorporates partial interaction between the concrete slab and steel component, as well as the degradation of the stiffnesses of the components of the composite beam prior to yield at elevated temperature. The generic technique that is developed is shown to agree with solutions reported elsewhere and provides a structural model for the response of a composite beam in fire with the potential for inclusion in prescriptive code rules for rational fire engineering based designs.

This paper reports on a study to extend a recently proposed direct displacement design (DDD) procedure for midrise engineered wood-frame structures and develop a set of factors for use in the procedure to meet specified performance levels with certain target probabilities. Representative index multistory building configurations were selected from the archetype buildings developed for the FEMA ATC-63. Seismic hazard levels and performance requirements recommended by ASCE 41-06 and modified for use in the National Science Foundation sponsored NEESWood project were used. The archetype buildings, originally designed using current force-based design procedures, were redesigned using the simplified DDD procedure (also described herein) with a range of nonexceedance (NE) probability adjustment factors $\left(C_{\text{NE}}\right)$ . Specifically, the design interstory shear forces and the sheathing nail spacings were determined for each structure designed using $C_{\text{NE}}$ . Nonlinear time-history analysis was performed for each archetype structure under the 2%/50 year seismic hazard level and peak interstory drift distributions were developed. The NE probability at the 4% drift limit was then plotted against building height and design charts were developed for each different value of $C_{\text{NE}}$ . Given the building height and desired NE probability, engineers/designers can select the appropriate minimum value of $C_{\text{NE}}$ using these charts. Additional analyses could be performed to consider other hazard levels and performance requirements. Using design charts of this type, engineers/designers are able to specify a target drift limit as well as a target NE probability when using the simplified DDD procedure. Thus, a true performance-based procedure for the seismic design of midrise wood-frame structures is described.

To achieve adequate flow and homogeneous concrete for precast, prestressed members, self-consolidating concrete (SCC) typically has higher paste and lower coarse aggregate volumes than conventional concrete (CC). The lower aggregate content of SCC can affect the shear capacity of concrete systems. This research performed 48 push-off tests to investigate the influence of SCC aggregate and paste volumes on the shear capacity and these results were compared with those obtained from similar CC samples. The variables included coarse aggregate type (river gravel and limestone), three coarse aggregate volumes for the SCC mixtures, and two target 16-h release strengths [34 and 48 MPa (5 and 7 ksi)]. The aggregate type, aggregate volume, and concrete strength were found to have significant effects on the aggregate interlock. Test results were used to propose new aggregate interlock models based on the modified compression field theory adopted in the AASHTO Load and Resistance Factor Design Specifications. More appropriate expressions have been developed to determine the limiting value of concrete shear strength for CC and SCC precast, prestressed concrete girders with similar mixture proportions, and a 28-day compressive strength greater than 70 MPa (10 ksi).

Distributed optical fiber strain sensors have attracted increasing attention in research and applications related to civil engineering because no other tools can satisfactorily detect the locations of unpredictable events. For instance, for crack detection, it is necessary to employ a fully distributed sensor because crack locations are a priori unknown. The Brillouin optical correlation domain analysis (BOCDA) system, a distributed sensor that offers high spatial resolution by using stimulated Brillouin scattering, has undergone significant development over the last decade, during which it has been used in a wide range of civil engineering applications. In this paper, we demonstrate how a BOCDA-based optical fiber strain sensor can be employed to monitor cracks in fiber-reinforced concrete. Crack monitoring is important for checking the structure of such high-performance concrete, which has enhanced strength and toughness since it incorporates fibers. In particular, early detection of tiny cracks is essential for preventing crack growth and dispersion. We carried out a concrete beam-bending test to detect crack-induced strain distribution during loading. For this purpose, we employed an improved BOCDA system that provides enhanced measurement length with high spatial resolution; hence, BOCDA can detect a tiny crack before visual recognition. Moreover, we demonstrate a field application of the BOCDA system to ensure a flawless pedestrian deck made of fiber-reinforced concrete.

In this paper, the performance of structures is modeled using lifetime functions. Specifically, the unavailability and redundancy are used as performance indicators, based on which optimum maintenance strategies are sought. Models that reflect the separate or combined effects of essential and preventive maintenance on the unavailability are presented. A novel optimization approach is proposed in which the problem is formulated to provide optimum maintenance strategies with either or both essential and preventive maintenance actions. Genetic algorithms are used to solve this problem. In this paper, multiple essential maintenance types and multiple preventive maintenance types are considered, and regular or irregular preventive maintenance time-intervals are considered. Furthermore, essential maintenance is treated as performance-based, i.e., essential maintenance is only applied when a performance threshold is reached, and an algorithm is proposed for conducting the optimization under uncertainty. Although applicable to any type of structure, the proposed approach is illustrated on a highway bridge example.

This paper investigates the behavior of a seismically excited benchmark building employing magnetorheological dampers operated by a model-based fuzzy logic controller (MBFLC) formulated in terms of linear matrix inequalities (LMIs). The MBFLC is designed in a systematic way, while the traditional model-free fuzzy logic controller is designed via trial and error by experienced investigators. It is demonstrated from comparison of the uncontrolled and semiactive controlled responses that the proposed LMI-based MBFLC is effective in vibration reduction of a benchmark building under various earthquake loading conditions.

In this paper, an optimization model for force finding of tensegrity systems with considerations of the geometrical stability condition, the unilateral property of members, and the evenness requirement of internal forces was developed. The simulated annealing algorithm was used to solve this optimization problem. Force finding of several typical tensegrity systems was carried out with the proposed method. It was found that the optimized solutions were very close to the analytical solutions and able to reflect the geometrical symmetry of the structures. It also verified that the proposed method is applicable to tensegrity systems under consideration including simple two-dimensional structures and complex three-dimensional multimodular structures.