Gian A. Rassati

Investigation on Effect of Transverse Reinforcement on Performance of Diagonally Reinforced Coupling Beams

This study investigates the effects of transverse reinforcement ratios on the post-elastic performance of diagonally-reinforced coupling beams in coupled core wall systems. Two coupled wall subassemblages, with two different transverse reinforcement detailings, were designed and tested under cyclic reversed loads. The design philosophy for both specimens is presented and discussed, and the detailing is compared with what is required by ACI 318-05. The experimental results are presented, with attention to the post-elastic performance of the specimens tested. Overall performance comparisons are made. Findings show that providing a higher transverse reinforcement ratio in a diagonally-reinforced coupling beam than that currently required by ACI 318-05 greatly benefits ductility and hysteretic stability.

A Performance-Based Design Approach for Coupled Core Wall Systems with Diagonally Reinforced Concrete Coupling Beams

Coupled core wall systems (CCWs) are lateral force resisting systems that can provide remarkable lateral stiffness for mid- to high-rise buildings, exceeding the lateral stiffness of isolated walls while providing the redundancy and force redistribution capabilities of framed systems. The lateral stiffness provided by CCWs largely depends on the type of coupling beams used to transfer forces between wall piers. Diagonally-reinforced concrete coupling beams are one of the more common details although composite alternatives (e.g., those using structural steel W-shapes, hollow structural steel sections, or embedded steel plates) or beams with rhombic reinforcement are increasingly being selected as viable alternatives. Despite the favorable behavior exhibited by diagonally-reinforced coupling beams in experimental studies, designing and constructing diagonally-reinforced coupling beams having practical span-to-depth ratios presents significant difficulties, impacting the use of CCWs as a viable lateral force resisting system. This paper presents a performance-based design (PBD) approach that allows the designer to successfully proportion a code-compliant CCW system that addresses the shortcomings related to the traditional strength-based design approach. A prototype building is designed following both approaches, and is analyzed both statically and dynamically. Results show that the PBD approach produces a code-compliant structure that satisfies the most pressing constructability constraints.

Prying Models for Strength in Thick-Flange Built-Up T-Stubs with Complete Joint Penetration and Fillet Welds

AbstractThe results of a series of finite-element (FE) simulations and experimental studies are used to develop two prying models that predict the failure strength of thick-flange built-up T-stub connections with complete joint penetration (CJP) and fillet welds. A parametric study based on identifying the major geometric and force-related parameters that vary within current acceptable steel fabrication and design practices is used to select the cases for analysis. The strength prying models predict the capacity of thick-flange built-up T-stub connections with CJP and fillet welds for the failure limit state of the partial yielding tension flange followed by bolt fracture. The accuracy of the developed strength models are verified with FE results of built-up T-stubs designed for full strength compared with existing models reported in the literature. Based on the results of this study, a refined design procedure that takes into account the partial yielding in thick-flange T-stubs is proposed.

New steel-concrete shear connection for composite bridges

This paper presents experimental and analytical research that was conducted on new connections “by adherence” for steel-concrete composite bridges. Their resistance is achieved by the frictional shear resistance of different interfaces positioned in a judicious manner. These connections make it possible to erect the structure quickly with full-depth precast concrete slabs, while the concreting works on site are limited as much as possible. Experimental results show that these connections exhibit a high resistance to horizontal shear forces and are very rigid compared to traditional connectors (headed studs). However, their ductility is limited. Based on the experimental results, a calculation model was developed and was used in a parametric study. Some results of the parametric study are presented and discussed in this paper. A simplified method for determining the resistance of these connections, design rules and recommendations for construction are proposed.

A Finite Element Study of Non-Orthogonal Bolted Flange Plate Connections for Seismic Applications

The current design approach for moment connections in many seismic specifications worldwide focuses on providing energy dissipation to achieve a collapse prevention objective. Most specifications only provide guidance for the design of beam-column connections in orthogonal configurations. However, it is not uncommon that for architectural reasons beams be required to frame into columns at an angle, either with respect to the horizontal (sloped connections) or with respect to a vertical plane (skewed connections), for the design of which little guidance is available. This paper presents a numerical study focusing on Bolted Flange Plate connections in non-orthogonal configurations. The response of these connections was compared to extant experimental results, using orthogonal configurations as a baseline. Investigating the connections response in terms of moment-rotation capacity, stress distributions, plastic strain demands, and plastic hinge locations, some recommendations for the design of non-orthogonal Bolted Flange Plate connections are presented. Secondarily, a study of the influence of specific details on the response of the connections was performed, resulting in practical detailing recommendations.

Seismic Performance of Steel MRFs with Partially-Restrained, Bolted, Beam-to-Column Connections through FE Simulations

Even though partially-restrained bolted beam-to-column connection systems are not explicitly certified to be used for moment resistance in current building specification jurisdictions, they represent a promising solution in modern steel moment resisting frames (MRFs), showing their significant potential to be able to mitigate some of the major drawbacks inherently related to the geometry of welded connections. In order to quantify the influence of this attractive solution, applicable both to new construction and to the retrofitting of existing structures, on the global response of whole MRF buildings under seismic loads, a numerical procedure, based both on refined three-dimensional solid and one-dimensional fiber-based finite element (FE) models, has been developed and validated using past experimental results. This validated numerical approach has been used to assess the seismic performance of T-stub connection systems within entire MRFs, in comparison with the response of other top-and-seat angle joints; a series of conventional and adaptive pushover and incremental dynamic analyses, accounting for material and geometric nonlinearities, has been carried out to quantify behavioral changes as a consequence of geometric variations in the connection system.

PERFORMANCE EVALUATION OF INNOVATIVE HYBRID COUPLED CORE WALL SYSTEMS

The paper presents an ongoing investigation of the cyclic performance of steel coupling beams in hybrid coupled core wall systems. Coupled core wall systems offer remarkable lateral strength and stiffness, and taking advantage of the favorable cyclic behavior of steel coupling beams makes the best use of all materials employed. Moreover, the inherent characteristics of the systems considered are ideal for an application of performance-based design approaches. Preliminary results are discussed from the standpoint of seismic performance, demonstrating the advantages of steel coupling beams and innovative details of coupling beams, conceived with reparability in mind, are presented. The design of a prototype structure is discussed, and a two-phase experimental campaign is described. It is anticipated that a hybrid, pseudo-dynamic analysis of the coupled core wall systems considered will show that the use of steel coupling beams in a performance-based design framework can deliver economical and safe structures with remarkable strength, stiffness, and ductility.

FINITE ELEMENT ANALYSES ON SEISMIC RESPONSE OF PARTIAL STRENGTH EXTENDED STIFFENED JOINTS

Extended stiffened end-plate bolted joints are widely used in seismic resistant steel frames. In the United States (US) this type of joint is seismically pre-qualified according to AISC 358. In Europe within the framework of the ongoing EQUALJOINT research project, prequalification criteria for different types of bolted joints are under development. Differently from the US approach, in the EQUALJOINT procedure both full and partial strength joints are seismically qualified. The experimental tests carried out within the EQUALJOINT project confirmed the effectiveness of these intermediate strength levels. Therefore, the aim of this work is investigate the possibility to extend this design approach to US joints. The results of a comprehensive parametric finite element investigation are described and discussed, showing the effectiveness of the proposed design performance criteria. 4952 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4952-4964

SEISMIC PERFORMANCE OF HIGH-RISE STEEL MRFS WITH OUTRIGGER AND BELT TRUSSES THROUGH NONLINEAR DYNAMIC FE SIMULATIONS

The work reported herein summarizes the results of a series of nonlinear dynamic FE analyses devoted to assess the main criticalities in the seismic response of high-rise steel MRFs with outrigger and belt trusses. Thirtyand sixty-storey planar frames, extracted from reference three-dimensional structures composed of an internal one-way braced core, are designed in accordance with European rules. The core consists of a CBF system, while outriggers are placed every fifteen stories to limit inter-storey drifts and second order effects. FE models able to account for material and geometric nonlinearities have been developed within an open source FE code, using inelastic force-based fiber elements to model structural members and equivalent nonlinear links to reproduce the behaviour of bolted beam-column joints and welded gusset-plate connections. Out-of-plane imperfections are explicitly included in the braces to allow for potential buckling mechanisms in both braces and gusset plates. NLTHAs have been performed, in comparison with response spectrum analysis, aiming to quantify the potential of such systems, when included in the lateral-force resisting system of modern highrise steel MRFs. Global and local performance have been investigated in terms of inter-storey drift and acceleration peak profiles and axial force-displacement curves and static-to-seismic load ratios in critical braces at different floor levels. Sensitivity to the structure height has been explored by comparing the response of the two prototype MRFs. Trends are discussed to show that, if accurately designed and detailed, these structural systems provide an optimum combination of stiffness and strength.

Performance-Based Design and Innovative Hybrid Systems to Overcome Design and Construction Challenges of Diagonally- Reinforced Coupling Beams

Coupled core walls (CCWs) are attractive lateral-force resisting systems with remarkable lateral stiffness. The extent of the lateral stiffness depends on the type of coupling beams used to couple the wall piers. Current building codes essentially imply the use of diagonally-reinforced coupling beams with practical span-to-depth ratio of two to four. Inherent difficulties associated with design and construction of diagonally-reinforced coupling beams are major impediments for CCWs, and are often cited as one of the primary reasons for selecting other systems despite the many advantages that CCWs offer. Performance-based design (PBD) paradigms and/or innovative systems offer viable alternatives to overcome these difficulties. This paper provides an overview of these two options.