Wiss Janney Elstner Associates

• Seismic performance of steel moment frames with fuse connections is studied. • Archetype buildings of 2, 4, 6, and 8 stories are designed for comparative analysis. • The effect of column design variations on seismic performance is analyzed. • Various fuse failure models are explored to assess their effects on performance. Fuse connections featuring replaceable components that yield before beams or columns have been proposed for steel special moment-resisting frames (SMRFs) as low-damage connection concepts in seismic systems. While several are prequalified or under review for prequalification in the United States, the impact of column design requirements and fuse behavior on seismic performance has not yet been thoroughly investigated. This study analyzed typical steel SMRFs of varying heights (2, 4, 6, and 8 stories) using a prequalified yield-type fuse connection, specifically the Simpson Strong Tie™ (SST) Yield-Link (YL)® connection. Current prequalified design procedures for this connection allow columns to be designed for larger overstrength demands without meeting certain seismic compactness limits. This study investigates the impacts of column design variations (i.e., column overstrength, compactness, and capacity-limited forces) on collapse performance. Nonlinear static pushover and incremental dynamic analyses revealed that designs that considered seismic compactness, even with relaxed overstrength demands, outperformed those with higher overstrength but no compactness requirements, particularly in taller buildings. However, since the shallower column sections for shorter buildings were more likely to meet width-to-thickness limits for highly ductile members, relaxing overstrength requirements could reduce the collapse margin ratios in SST-YL SMRFs. These results indicate that there is potential to consider modified column design requirements for SST-YL connections, offering a cost-effective approach to improving structural resilience without compromising seismic collapse performance.

Estimating the drift capacity (DC) of reinforced concrete (RC) structural walls is crucial to assess seismic performance of buildings in earthquake-prone regions. Numerous investigations have been conducted on the subject. Nevertheless, most of these investigations focus on walls without prior damage and a single expected earthquake. Recent tests conducted on RC walls suggest that displacement history does not affect DC, if the maximum amplitude of previous cycles is smaller than a threshold, regardless of the number of applied cycles. How to define such threshold and how prior cycles with amplitudes exceeding it affect DC remains unclear. This study assessed the effect of cyclic displacement history—or displacement cycles—on the DC of RC structural walls, using a statistical analysis. Results indicate that DC decreases as the intensity of cyclic displacement history increases. Nevertheless, this decrease is considerably smaller than differences between measured values of DC and estimates obtained using available empirical formulations and a calibrated machine learning algorithm.

Owing to its unique mechanical properties, chemical resistance,and ion conductivity, Nafion is one of the most widely used polymerelectrolytes. In hydrogen fuel cells, it constitutes both the macroscopicmembrane separating the anode and the cathode, and as a thin film,Nafion appears as a binder in the catalyst layer where conductiveionic pathways must intimately interface with platinum catalyst particles,electrically conductive carbon particles, and porous surfaces thatfacilitate the transport of gases. Residing at the intersection ofthis diverse range of materials, the ionomer’s interfacialstructure influences interfacial impedance and thus device performance.This interface structure has been widely investigated on model surfaceswith neutron reflectometry and other techniques, resulting in thediscovery of a multilamellar structure at the interface with hydrophilicmaterials, or a single water-rich layer at the interface with, e.g.,metals, favoring tangential vs perpendicular ion transport, respectively.Here we demonstrate that self-assembled monolayers, SAMs, which cancoat various surfaces, can control whether single or multiple lamellaeoccur. These interfacial structures can be further modified throughacid–base interactions by protonating the terminal amine groupof a SAM at low pH. This establishes a methodology to control theinterfacial ionic transport pathways in Nafion and determine the interfacialimpedance.

Hooked bar lap splices are used in accelerated bridge construction (ABC) operations even though this detail is not addressed in the AASHTO LRFD bridge design specifications. To address this knowledge gap, this paper synthesized the current state of practice of such splices in the US to provide practitioners knowledge of how to use, design, and construct hooked bar lap splices. To accomplish this objective, a survey was distributed to all state Departments of Transportation (DOTs) of the US. Thirty-one responses were received. After discovering that more than half of the survey respondents had some degree of experience using hooked bar lap splices, it was decided to conduct follow-up interviews with representatives from three state Departments of Transportation that had compelling experience with this detail. These efforts revealed that the predominant application of hooked bar lap splices was in the connections of precast deck elements. However, these splices also were reported to have been used within continuity diaphragms, to connect large precast elements (e.g., bent caps), and in cast-in-place construction to reduce required splice lengths. Most DOTs preferred the use of such splices in a noncontact configuration to avoid interference during alignment of precast elements. Furthermore, in the absence of dedicated design guidance and relevant test data, hooked bar lap splices typically have been designed using code provisions for lap splices of straight bars and the tension development length of hooked bars. Despite issues with constructability such as reinforcement congestion within closure joints and interference of hooked bars during splice alignment, practitioners believe that hooked bar lap splices offer a number of advantages in ABC operations. Design examples regarding the use of hooked bar lap splices to connect precast concrete decks and bent caps were developed to complement the survey results.

Despite the historical tendency toward proportioning and spacing braces based on rules of thumb, modern specification guidance stipulates that cross-frame design be supported with a rational analysis, which is commonly aided by computer software. While cross-frame research has advanced over the last 30 years, the relatively vague nature of specification language related to rational analysis is still utilized and often misunderstood by engineers leading to uneconomical chase-your-tail design solutions—particularly related to the fatigue limit state. To improve the design specifications and economy, an extensive analytical parametric study was conducted to quantitatively investigate the sensitivity of load-induced cross-frame response in varying bridge geometries. The study included multiple three-dimensional analyses on 4,104 unique steel I-girder bridges. Among other observations, the results demonstrated that load-induced cross-frame forces are generally higher in heavily skewed systems. From these studies, two primary recommendations are proposed to improve specification guidance on fatigue design of cross-frames. First, designers can avoid overly conservative and iterative designs by utilizing staggered and/or discontinuous cross-frame configurations, thereby alleviating force demands in heavily skewed systems. Second, the study concluded that refined analyses are not warranted in straight bridges with little to no support skew since cross-frame force magnitudes are generally not significant. Geometric limits based on skew and connectivity indexes are proposed to serve as the delineation between when a refined analysis is recommended.

Spontaneous glass breakage from nickel sulfide inclusions continues to plague facades with tempered glass. The situation is particularly concerning when the tempered glass is used as an exterior lite on building facades, where the risks associated with glass fallout are significant. One strategy often considered to mitigate such risks is the use of an exterior anchored safety film; however, the efficacy of an unanchored exterior film requires validation. The post-breakage behavior of structural silicone-glazed insulating glass units with unanchored exterior-filmed tempered glass lites was explored by performing cyclical pressure testing. Pass/fail test criteria were nominally taken from ASTM C1048. Test results were used to estimate maximum wind speeds that the filmed glass could reliably withstand at the time of nickel-sulfide-induced fracture. The estimated wind speeds considered the specific structure and building site. Using a similar process, decisions regarding the efficacy of unanchored safety film can be made for other applications.