Practice Periodical on Structural Design and Construction

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Old steel arch bridges commonly need rehabilitation interventions because of their insufficient lateral resisting capacity against seismic loads. A localized strengthening method is not always applicable to such bridges because of high costs and the lack of convenient access to the structural members, and replacement of the existing arch supports with base isolators is extremely difficult and risky. As an alternative and convenient retrofitting method, energy dissipation systems in the form of nonlinear viscous dampers (NVDs) can be adopted. This study analyzed NVDs localized within the end bracing members of a steel arch bridge (Qotour Bridge, Iran) as a case study. Because the selection of NVD properties and the optimal location of the NVDs require several extremely time-consuming nonlinear analyses, a design strategy was outlined using linearization of the structural system. The linearization was performed by developing novel concepts of equivalent damping ratio and damping correction factor for the structure rehabilitated with localized NVDs, and the proposed design strategy was applied to the real steel arch bridge. The complimentary nonlinear analyses (nonlinear time-history and pushover analyses) conducted showed that the proposed design method is reasonably accurate in the prediction of the maximum response of the rehabilitated bridge. Moreover, the results showed that by using the proposed linearization method, the NVD characteristics can be adjusted suitably so that the seismic demand on the existing members and connections remains below an allowable limit, and the nonlinear deformations and energy dissipation are localized mostly in the NVDs.

Raft foundations can be analyzed using the conventional, Winkler, and continuum methods. In the conventional method, it is assumed that the raft is rigid and settles uniformly. In the Winkler method, commonly employed in structural analysis software packages, soil is represented by a series of springs. On the other hand, in computer-aided continuum analysis, soil below the raft is modeled using solid elements available in finite element–based software. In the present study, analyses of the raft as a single unit and the raft together with the superstructure as a combined unit are carried out separately for a wide range of soil strength parameters employing the Winkler and continuum methods. The results of the analyses and subsequent designs were compared for different models. The variations in the quantity of reinforcement required for the raft and superstructure, corresponding to changes in soil stiffness values in different modeling methods, are investigated. Useful recommendations are presented to increase the effectiveness of Winkler model for structural design. The need for modeling the raft and superstructure as a combined unit is also highlighted.

Keeping bridges in good condition during their service lives continues to be a challenge. Additionally, the condition assessment of concrete bridge decks is complicated as it is influenced by several factors. Environmental factors are among the main reasons behind the deterioration of concrete bridge decks. Therefore, studying the impact of environmental factors is a significant part of the condition assessment of concrete bridge decks. In this study, the condition ratings of concrete bridge decks were used to investigate whether there is a universal model that can represent the impact of environmental factors on deterioration rates of concrete bridge decks in the US. The results showed that the best deterioration model varied from one state to another, and there was no universal statistical prediction model that can be developed for all states. Additionally, it was observed that the Weibull distribution method was the best model for the Southern, Southeast, and Western Regions, while the lognormal method was the best for the Northeast, Midwest, and High Plain regions. Furthermore, it was concluded that environmental factors have a significant impact on the deterioration of concrete bridge decks. This paper will help transportation network agencies better plan for the maintenance, rehabilitation, and reconstruction actions and funding. Additionally, it can help in establishing optimal guidelines to maintain bridges based on their climatic regions.

Curved surface sliders are generally preferred for the seismic isolation of buildings because of their technical features, such as the fact that the value of the vibration period is theoretically independent of the mass. Given the experimental evidence that indicates that the isolated system did not work under low seismic actions, in this paper, the influence of the static friction on the global behavior of some structures is studied in detail. By adopting a suitable model of friction, the onset of motion is analyzed with reference to simple isolation systems in which the influence of the friction values and its variability among the isolation devices are analyzed. The results pointed out that the behavior of curved surface sliders is not independent of the vertical load and highlights the importance of a suitable choice of the design friction, which must be different for devices with different vertical loads.

It is becoming increasingly common to employ tuned sloshing damper (TSD) systems to reduce the wind-induced motion of tall buildings due to their affordability and apparent simplicity. However, TSD systems are relatively new to the high-rise construction industry, and, due to their unfamiliarity, design and construction teams may perceive these devices as having considerable risk. Since the implementation of these systems requires a performance-based design approach (rather than a prescriptive approach) to ensure serviceability performance objectives are achieved, knowledge of their function and operation is paramount to their efficient design and installation. The goal of this study is to reduce the perceived risks by describing the function of TSDs, as well as the practical aspects of the design and installation process. The process is described in four phases: concept design, detailed design, construction, and tuning and commissioning. The key tasks associated with each phase are defined and common challenges identified. This paper does not present new theory to further advance the TSD research; instead, it summarizes current theory and presents practical guidance accumulated from years of experience with the design, installation, and as-built performance verification of many TSD systems.

The present work focused on the determination of the collapse load and failure mode of a reinforced concrete (RC) of collapsed framed structure constructed in the South of Italy that failed in 2004. Information available included the results of an extensive experimental test campaign for the determination of mechanical properties of concrete and steel bars of beams, floors, and columns involved in the failure. Moreover, drawings of the original design with construction details and design rules valid in Italy at the time of construction were found. A simple monodimensional beam model for prediction of load-deflection curve, able to include degradation of constituent materials (concrete, steel, and bond), was developed. Ultimate load predicted analytically at the time of the failure was very close to that estimated on the structures at the time of collapse and due to the self-weight justifying the failure of building. Results obtained highlighted that concrete degradation phenomena were the main causes of collapse. In addition, numerical analyses with Response (2000) and Atena 3D (2004) were carried out to predict ultimate load, failure mode, and crack patterns at failure. Results obtained numerically showed good agreement with available experimental data and with the proposed one-dimensional model. Comparison between simplified analytical and numerical responses showed that although the use of refined nonlinear finite-element models give much more detailed information with respect to the one-dimensional model, the latter can be very useful for preliminary check of the structures.

The effect of vertical baffles as the passive control in liquid storage tanks (LSTs) on the reduction of seismic responses was investigated for bidirectional earthquake excitations. Various baffle configurations were considered for arriving at an optimum coupled arrangement of baffles in the LSTs. For this optimum arrangement of baffles, the change in various responses was studied for several parameters, namely the type, peak ground acceleration (PGA), and angle of incidence of earthquakes. A numerical study was conducted with two flexible concrete LSTs with dimensions $6\times 6\times 4.8$ and $12\times 6\times 4.8\mathrm{m}$, and with a water level of 3.6 m in both LSTs. The responses included the maximum percentage change in base shear, overturning moment, top-board displacement, hydrodynamic pressure, and sloshing height. The results of the study showed that (1) with the optimum arrangement of baffles, a reduction on the order of 70% can be achieved in the sloshing height, (2) the type of earthquake does have some significant effect on response reductions, and (3) both PGA and angle of incidence of earthquakes have moderate effects on response reductions.

The design of conventional curved surface sliders (CSSs) uses appropriate selections of effective radius and friction coefficient. These two design parameters are commonly optimized for the design basis earthquake (DBE). As a consequence,, efficient structural isolation for weak and frequent earthquakes is hardly possible on the one hand and the isolator relative motion due to the maximum considered earthquake (MCE) becomes unacceptable large on the other hand. This trade-off problem is solved by adaptive stiffness and damping behaviors. The concept of the adaptive CSS is described, and its seismic performance is computed by nonlinear time history analysis using a nonlinear and experimentally validated model. The results demonstrate that the adaptive CSS significantly enhances seismic structural performance.

Cold-formed steel (CFS) can be a competitive light-frame solution for low-rise buildings, particularly when noncombustible construction is required. In noncombustible semiballoon frame construction, installation of wall sheathing to the top of a wall such that the sheathing is sandwiched between the floor ledger track and the wall framing has been gaining more interest from contractors—a detail that may affect the shear strength of the ledger-to-wall connection. In this paper, the results from a series of tests aimed at exploring the strength of alternative noncombustible floor-to-wall gravity load shear transfer ledger details—with wall sheathing interposed between the wall framing and the ledger—are presented. Data from the tests permits a comparison of connection performance between the interposed and noninterposed wall sheathing conditions. These comparisons show that the alternative interposed details provide equal or higher strength compared to the noninterposed condition.

The commonly-used viscous damping approach, Rayleigh damping, has been shown to develop excessive damping forces in the nonlinear response history analysis (RHA) of fixed-base structural systems. These forces are referred to as the initial stiffness. While the incorporation of foundation flexibility plays an important role on the seismic performance of the structures, this effect has been ignored in past studies that examined Rayleigh damping. In this study, the elastic and inelastic RHA were applied on fixed- and flexible-base structural systems to (1) address the effect of foundation flexibility on the resulting Rayleigh damping ratios; and (2) evaluate the effect of various damping formulations on the structural response. A structural analysis was performed on 10-story steel special moment-resisting frames. The results showed that the incorporation of the flexibility of the foundation increased the stiffness proportional ratio of Rayleigh damping, which, in turn, increased the total damping ratio compared to the fixed base condition ratios. Mass proportional damping was not affected by foundation flexibility. Consequently, initial stiffness-based proportional damping resulted in the largest dynamic response compared to the other damping approaches for the fixed base systems. Per contra, the structure was heavily damped when stiffness proportional damping was in control for the flexible-base system. In contrast, mass proportional damping produced the largest lateral deflection and interstory drift for the flexible-base systems. The flexible-base story shear was not significantly affected for the different components of Rayleigh damping.

Framed-foundations supporting rotary machines are either supported on a raft foundation or on a pile foundation, depending on the type of soil conditions, loadings, and other functioning requirements. Influence of soil–structure interaction (SSI) is either completely neglected or rigorously considered in the practice. Neglecting the SSI may not always be safe, and on the other hand, rigorous analyses are computationally expensive. In this paper, the SSI problem in the machine foundation is formulated using an analytical model with a lumped-mass approach and the results are compared with a three-dimensional (3D) finite-element (FE) model. The results obtained through the FE modeling technique are validated using existing results and then adopted in further analysis. From the results, it is found that simplified methods can be used for foundations resting on rock-to-dense-soil condition; however, the FE analysis is mandatory in the case of stiff-to-soft-soil conditions. It is also observed that the effects of SSI reduce the natural frequency significantly in the case of a raft-supported framed-foundation resting on soft soil strata. Pile-supported framed-foundations are considered to be a better solution in the case of soft soil conditions to control the vibrations of the framed-foundation in comparison with the raft foundations. The suitability of each foundation type for different soil conditions for limiting the displacement within the permissible values is also discussed.

A simple yet accurate approach to evaluate the seismic performance of a torsionally coupled multistory building isolated by nonlinear isolators and subjected to strong ground motions is presented in this paper. In this study, the shear-type torsionally coupled multistory building controlled by the resilient friction base isolation (RFBI) system is presented. The governing equations of motion of the proposed torsionally coupled isolated structure are derived and solved using Newmark’s step-by-step method of integration. MATLAB codes are developed to evaluate the nonlinear responses of the proposed isolated system. Energy dissipation in this structural system occurs due to the presence of frictional force, which is developed through the relative velocity of the base isolator concerning the ground. Detailed numerical results are illustrated to deliver an exact idea regarding the mitigation of structural responses in the presence of the RFBI system during earthquake events. To illustrate the significance of the controlled device, response histories considering the controlled and uncontrolled system as well as other parametric results are plotted. The results obtained from the analysis are feasible and useful for practical design use.

The double-concave curved-surface slider isolators are tribological systems composed of the assemblage of three rigid bodies that include two concave spherical plates and a straight cylinder with convex bases coupled with the former two and placed in between themselves. They originally spread under the name of double friction pendula (DFP), and compliant sliding was expected to take place along the coupled surfaces, during an earthquake. Compliant sliding means that it would take place with uniform distribution of geometrical contact and stresses in compliance with a supposed pendulum behavior. However, since earthquakes impose a horizontal kinematic history to the lower plate, the fulfillment of geometrical compatibility suggests that the relative movement between those three rigid bodies may only take place by a recursive alternation of sticking and slipping. Where this latter, assuming that the three components remain rigid, would take place not in a compliant manner but, on the contrary, would be concentrated along the extremities of one diagonal only of the pad. Since the three constitutive components of the double-concave curved-surface slider devices are expected to remain rigid during their relative movement, multibody modeling techniques currently used to simulate machines and mechanisms can be applied to the case study. For this reason, and in order to have more arguments to appraise the validity of the suspect above, the multibody kinematic equations were developed and applied for both supposed compliant sliding and expected stick-slip for two prototypes, a flat and a squat one. With the objective to contribute to the optimization of these devices, parametric numerical studies were also carried out with both approaches to help figure out respectively if the stick-slip effect is to be expected and in which circumstances it can be minimized. The obtained results herein presented neglect acceleration and forces for the sake of brevity and for the time being, but the complete dynamics will be presented in another work.

This paper deals with the structural design aspects of support systems of industrial reactors. An overview of the geometric characteristics of vertical and horizontal reactors is presented. Finite element strategies to model the load transfer mechanism and soil/structure interactions are also described. Design parameters required for the foundation and pile supports are identified using various loading conditions. Design recommendations based on extensive analyses are proposed for vertical absorber stripper (VAS) and horizontal catalytic (HC) reactors. The proposed guidelines are cost-effective and can be utilized by engineers in practice to design the support system. The scope of the paper is limited to structural engineering design and construction aspects. The chemical and mechanical design aspects are not covered within the scope of this paper.

Shelf angles are attached to the structural system and are designed and detailed properly to provide support for veneer walls. They are secured to concrete or masonry structural systems through anchor bolts. In some applications, shelf angles are bolted or welded to steel structures. Shelf angle design requires proper detailing and sizing the angle and connecting anchors (in concrete and masonry attachment) and bolts or weld (in steel system attachment). In masonry and concrete attachments, spacing between anchors is determined by examining the veneer wall’s ability to span itself between the two adjacent anchors or to act as a cantilever over the edge beyond the last anchor. Design of anchors requires following the procedures outlined by the American Concrete Institute and is achieved by selecting a proper diameter and embedment length with considerations for several modes of failure in tension and shear. This paper presents an overview of the procedure used for shelf angle design and detailing as well as attachment to concrete and masonry. This is then supplemented with three example problems. Example 1 illustrates the method for sizing an angle to support a veneer wall, while Examples 2 and 3 demonstrate anchor design for shelf angle attachment to concrete and masonry, respectively.

Prestressed soil anchors are utilized as a part of a deep excavation support system of a construction site in Turkey. After the completion of the construction, temporary soil anchors used for this site were no longer needed and, therefore, idle. Another construction about 2 years later started near this site. For the deep excavation support system for the second site, the soil anchors of the first site were used as tendons. After the construction was completed at the second site, the tendons became idle too. In this case study, the selected procedure provided several advantages to the construction in the second lot in terms of time and the overall cost of the excavation support system. The implementation of this system requires as-built information on the temporary support system of the first site. Besides, the free stressing length of the anchor utilized for the wall at the first lot is supposed to be longer than the distance to the second wall that is planned to be built at the neighboring lot so that the stressing is possible. Soil anchor strands used for the first construction site are to be intact. This paper presents the application of previously installed soil anchors as post-tensioned tendons and also the approach for the tendon post-tensioning load.

Transportation projects require unique and specific management processes, making an investigation of the particular dimensions of project management relevant to such projects necessary. The primary objectives of this study were to (1) explore the project management dimensions related to the successful delivery of transportation projects, and (2) analyze the existing project management processes of state DOTs in the US to understand current practices as well as existing weaknesses and potential future opportunities. First, by reviewing and collecting construction project management dimensions from the existing literature, 12 transportation project management dimensions were extracted. The dimensions identified were then used as a framework to collect and analyze DOTs’ publicly available manuals and guidelines. The results of this study provide insight for project managers and policymakers in the transportation industry to better understand the dimensions of construction project management required for successful transportation project delivery, existing weaknesses, and potential future opportunities for USDOTs.

The traditional approach of assuming that the throat of the fillet weld resists the load, regardless of the direction of loading is followed in Indian steel code IS 800. However, based on experimental research, the American Structural Welding Code-Steel, the American Institute of Steel Construction code, and the Canadian code have modified the equations to consider the direction of loading. These provisions are discussed, and three examples are also included to show that economic design of weld material can be achieved by using these provisions. Although the end fillet may resist more loads, it may have less ductility than the side fillet. Hence, the designer should exercise caution while using the end fillet, especially when ductility is required in situations where overloading is likely to occur.

The behavior of cold-formed steel (CFS) built-up members is fascinating, and owing to its advantages, the necessity of using built-up members is increasing in construction practice. However, as per the current design specifications of the American Iron and Steel Institute (AISI), there is no explicit design method for CFS built-up members. The objective of this investigation is therefore to examine the appropriateness of using the current AISI design method for CFS open or single cross-section members toward the design of built-up members with slender unstiffened flange elements subjected to bending. The investigation results indicate that the previously suggested design procedure (built-up elastic buckling model with double flange element) results in unconservative design predictions compared to the experimental results ($M_{\mathrm{EXP}}$ versus $M_{\mathrm{DSM}}$). The reason for the unconservative design prediction by AISI expression with the previously suggested procedure is due to the overestimation of the critical elastic local buckling stress and incorrect failure mode prediction of the built-up cross section, which is a key input to the direct strength method (DSM). Hence, modified design equations and procedures are suggested for the CFS built-up beams with slender unstiffened flange elements. The modified design procedure is formulated from the investigation of failure modes. It is also shown that the newly proposed design equation with the suggested procedure for determining the local buckling stress for slender unstiffened flange elements is reliable.