Primary Lateral Load Research Articles

Experimental and analytical studies on the behavior of connections between high-rise braced steel storage racks and the spine bracing

The primary lateral load resisting system of the high-rise braced steel storage racks is the spine bracing located at a short distance away from the rear rack frames. The connections between the rack frames and spine bracing, which transmit the horizontal stabilizing forces, dictate the effectiveness of the spine bracing and the global performance of the entire high-rise racking system. The first part of this paper experimentally establishes the behavior of the connections between the racks and the spine bracing under lateral loads, utilizing four groups of three nominally identical test specimens. A digital image correlation (DIC) measurement system is employed to generate comprehensive data associated with the behavior of individual components of such connections. The behavior of the connection components is quantified and discussed based on the three-dimensional deformation field recorded by the DIC system. The second part of this paper develops a component-based elastic analytical model for the connections between the racks and the spine bracing under consideration. The endplate spatial flexural bending mechanism, as well as the upright cross-section distortional behavior, are explicitly considered by the analytical model. The contributions of each individual component towards the total deformation of the connections are quantified. The paper concludes with design and construction recommendations for the enhancement of the connections between the racks and the spine bracing, while recognizing the limitations of this research.

Nonlinear Seismic Analysis of Perforated cold-formed steel shear wall with Upright Section

During the last few decades, cold-formed steel (CFS) is extensively used in mid- and low-rise housing due to the increasing demand of rapid constructions along with its various advantages in comparison with other structural material. Cold-formed steel framed shear walls (CFSFSW) are most common and primary lateral load resisting system. However, adopting it in the seismic zone is difficult, especially because many design components remain open. In this research an effort has been made to design the shear wall system with both unperforated and perforated upright sections using nonlinear static analysis method. In ABAQUS, a general-purpose finite element analysis software, three-dimensional models using shell elements are used to simulate a shear wall system. A comparative study regarding the lateral load capacities with respect to maximum allowable lateral deflection including different parameters like column sections, thickness and perforation arrangements are presented here. It was found that increasing thickness and including Chanel stiffeners improves the lateral strength of original upright section. The developed modelling protocol helps to estimate its lateral performance under earthquake with reasonable accuracy.

Impact of bi-directional loading on the seismic performance of C-shaped piers of core walls

Reinforced concrete structural walls are commonly used as the primary lateral load resisting system in modern buildings constructed in high seismic regions. Most walls in high-rise buildings are C-shaped to accommodate elevators or other architectural features. C-shaped walls have complex loading and response including: (1) symmetric response in the direction of the web, (2) asymmetric response in the direction of the flange and (3) high compression and shear demands when used as a pier in a coupled-wall configuration. A research study was conducted on C-shaped walls tested under (1) uni-directional and (2) bi-directional loading of an isolated walls and (3) bi-directional loading of a c-shaped pier in a coupled wall system. Each of the walls failed in flexure with strength loss resulting from low-cycle fatigue of the boundary element longitudinal reinforcement with buckling followed by fracture. The damage progression was as follows: (1) cracking at the wall-foundation interface, (2) concrete spalling in the web, (3) buckling and fracture of web reinforcement, (4) spalling in the flanges, (5) buckling and fracture of the bars in the boundary elements. Concrete spalling and steel bar damage occurred at lower strong-axis drift levels for the bi-directionally loaded, resulting in lower drift capacities for these loading protocols. However, for the strong-axis direction, bi-directional loading does not reduce flexural or shear effective stiffness values suggesting that current values are appropriate for design and evaluation of buildings with c-shaped walls.

Seismic Fragility Assessment of Non-ductile Reinforced Concrete Buildings in Australia

ABSTRACT This study aims to assess the seismic performance of typical reinforced concrete buildings constructed in Australia before the enforcement for seismic design. The response of both the primary lateral load resisting system and the gravity load resisting system is considered. A brief description of the modelling approaches adopted to simulate the response of the buildings’ components is provided. Nonlinear time history analyses are conducted and “cloud analysis” is used to develop the probabilistic seismic demand models. The results from the fragility assessment suggest that the low-rise buildings located on soft sites are the most vulnerable buildings.

Seismic performance of mortarless reinforced masonry walls

Reinforced masonry walls are commonly used as a primary lateral load resisting system in buildings in regions of moderate or high seismicity. Mortarless reinforced masonry (MLRM) walls are constructed using concrete masonry units placed without mortar and then interconnected by concrete grout. The absence of mortar can overcome several issues during the construction of conventional reinforced masonry walls. Previous research mainly focused on mortarless systems using three-dimensional interlocking blocks without vertical reinforcement. In this study, a total of six MLRM walls were constructed and tested under cyclic loadings to investigate their seismic behaviour. Experimental parameters included axial load ratio, shear span ratio, and vertical reinforcement ratio of the walls. Test results showed that the MLRM walls exhibited high stiffness, good deformation capacity, and reasonable energy dissipation capacity. The response of all six walls under cyclic loadings was controlled by 3–4 cracks formed at bed joints between the concrete masonry units, and their failure was dominated by flexure with the occurrence of slight shear sliding. The load-displacement envelope, strength, and energy dissipation of all tested MLRM walls are discussed.

Role of punching shear reinforcement in the seismic performance of flat slab frames

Horizontal cyclic loading tests of flat slab–column specimens indicate that a considerable enhancement of the drift capacity can be achieved by introducing punching shear reinforcement. However, seismic design codes either do not recommend or do not cover buildings in which flat slabs are part of the primary lateral load resisting system. Nonetheless, flat slabs are popular, even in earthquake-prone areas. The purpose of this paper is to contribute towards a better understanding of the benefits and limitations of using punching shear reinforcement in the seismic performance of such structures. To this end, nonlinear static analyses and a set of fragility functions are derived for two reinforced concrete three story frame models. To minimize modelling uncertainties, the numerical models are calibrated based on two laboratory specimens (one without punching shear reinforcement and the other with headed studs) tested under reversed horizontal cyclic loading. The results show that the performance of the frames can be improved by introducing punching shear reinforcement. However, it is shown that the inherent flexibility of slab–column connections under lateral loading remains a limiting factor even when punching shear reinforcement is provided.

Steel framed structures with cross laminated timber infill shear walls and semi-rigid connections

In recent years, hybrid steel-timber structures are seeing an increasing use in modern building construction at a competitive price. Cross-laminated timber (CLT) is a prefabricated multi-layer engineered panel wood product, manufactured by gluing layers of solid-sawn lumber at perpendicular angles. Their orientation results in excellent structural rigidity in both orthogonal directions. CLT construction materials are used not only for flooring systems and roof assemblies, but CLT infill shear walls are also gaining a lot of interest as a promising alternative for sustainable primary lateral load resistance systems. This paper extends the current research background on hybrid steel-timber structures. To achieve that, this work is conducted in such way as to explore the potentiality of incorporating CLT infill shear walls within steel framed structures with semi-rigid connections (STSW). In particular, a three-dimensional finite element model using the general-purpose finite ele-ment program ANSYS is generated herein to study the mechanical behaviour of a single-bay, two storey STSW system with semi-rigid connections. Analytical results show that the presence of CLT infill shear walls can significantly improve the performance of moment-resisting frame systems, for multi-storey buildings. Moreover, it is observed from the extended parametrical study that the STSW systems show better performance when an appropriate plastic moment ratio index is defined.

Racking stiffness and strength of cold‐formed steel frames braced with adhesively bonded glass panels

ABSTRACTIn cold‐formed steel building construction, cold‐formed steel shear wall panels (CFSSWPs) are used as primary lateral load resisting components, that maintain the stability and the integrity of the structure. Traditionally, a CFSSWP consists of a cold‐formed steel frame with structural sheeting, such as oriented strand board (OSB), gypsum wall board (GWB), plywood or other, screwed onto it. These type of elements have some unique properties, such as high elastic stiffness, large displacement ductility, etc. On the other hand, as the studs are closely spaced – a value of 60 cm for the spacing is common – only small openings are present, hence transparency is limited. To increase the transparency of cold‐formed steel buildings, which is a tendency in contemporary architecture, load‐bearing capacities of glass can be utilised by bracing the frames with glass instead of traditional sheeting. The conventional two‐component structural silicone Sikasil® SG‐500 is considered for the load‐bearing cold‐formed steel‐glass connection. In this research, the racking behaviour of 1.5 m by 3.5 m cold‐formed steel frames onto which glass panels are circumferentially bonded on both sides is determined by means of experimental tests. This paper reports about the conducted experiments and the obtained data. From the tests, a value of 35.25±0.452 kN/m was obtained for the racking strength of the considered hybrid cold‐formed steel‐glass panels. A comparison with traditional CFSSWPs showed that the hybrid element can obtain similar racking strengths. Therefore, the study revealed the potential of hybrid cold‐formed steel‐glass elements using structural silicones to provide sufficient in‐plane lateral stiffness and strength.

Application of steel-concrete-steel sandwich deep beams into coupled shear walls

Coupled shear walls are widely used as the primary lateral load resisting element in high-rise buildings. But the coupling beams, which are often designed as deep members, usually suffer from brittle shear failure. The steel-concrete-steel sandwich deep beams showed high bearing capacity and great ductile performance during shear failure. Therefore, it is proposed that the steel-concrete-steel members can be used into deep coupling beams instead of conventional reinforced concrete members, to improve the shear strength and deformability. The shear failure of steel-concrete-steel deep beams is characterized by plastic yielding of the outer steel plates in the triangular areas, rather than concrete diagonal crushing. Reliable shear transfer paths are maintained by the interaction between the outer steel plates and the diagonal concrete struts, so excellent strength and ductile performance can be expected after critical diagonal cracking. The triangular failure areas are able to dissipate seismic energy, thus effectively avoiding overall collapse. The shear strength of steel-concrete-steel deep coupling beams is developed with simple expressions.

Buckling-Restrained Braces (BRB) Seismic Design - A Consulting Engineer’s Consideration

There is no standard for the design of Buckling-Restrained Braces (BRBs) frames in New Zealand. Consequently, a consulting engineer would need to consider a range of overseas design standards and latest research findings and incorporate into a New Zealand code-compliance framework. This “Alternative Solution” pathway to satisfy the New Zealand Building Code means peer review and agreement with peer review is required. This paper describes the design journey and technical challenges the authors had in the seismic design of the BRB for the New Zealand International Convention Centre (NZICC). BRB frames are used as the primary ductile lateral load bracing system, acting in parallel with the moment-resisting frames formed by the primary cruciform columns and storey-deep trusses. Due to the vertical irregularity and a dual-system structure, a direct displacement-based design (DDBD) approach was used in parallel with a more convention code-compliant force-based design, to derive the BRB design actions. The design of the BRB connections, in particular the gusset design is particularly challenging due to the diverging views and numerous methodologies available. We have considered several analytical methods for the BRB connection design and commissioned two full-scale testing of the critical BRB and the gusset connection. Lessons learnt

Displacement-based seismic design of flat slab-shear wall buildings

Flat slab system is becoming widely popular for multistory buildings due to its several advantages. However, the performance of flat slab buildings under earthquake loading is unsatisfactory due to their vulnerability to punching shear failure. Several national design codes provide guidelines for designing flat slab system under gravity load only. Nevertheless, flat slab buildings are also being constructed in high seismicity regions. In this paper, performance of flat slab buildings of various heights, designed for gravity load alone according to code, is evaluated under earthquake loading as per ASCE/SEI 41 methodology. Continuity of slab bottom reinforcement through column cage improves the performance of flat slab buildings to some extent, but it is observed that these flat slab systems are not adequate in high seismicity areas and need additional primary lateral load resisting systems such as shear walls. A displacement-based method is proposed to proportion shear walls as primary lateral load resisting elements to ensure satisfactory performance. The methodology is validated using design examples of flat slab buildings with various heights.

An Analytical Modeling Framework for Primary Lateral-Load–Resisting Unreinforced Masonry Walls

This paper investigates an analytical modeling framework for the primary lateral-load–resisting walls, including out-of-plane effects, in unreinforced masonry (URM) building structures. Integral to each URM wall model with door and window perforations is a macro-element that represents each solid masonry panel within the structure. The macro-element consists of multiple discrete elements for modeling different characteristics of URM wall behavior, including sliding, rocking, and diagonal tension/compression. Validation of the model is conducted through comparison of the analytical predictions with observed behavior from previous tests available in the literature. The simplicity of the macro-element modeling approach, together with its material/geometry-based ability to predict URM behavior, permits the extension of this framework to a wide range of analyses (e.g., numerous ground motion records, variable material properties, diverse geometrical features, and building layouts) to support a semiautomatic seismic assessment for URM typologies.

Deteriorating hysteresis model for cold-formed steel shear wall panel based on its physical and mechanical characteristics

Shear wall panels (SWP) are the primary lateral load resisting elements in cold-formed steel (CFS) structures. In this paper, smooth hysteresis models that take into account strength and stiffness degradation, as well as pinching effect have been developed and implemented in OpenSees software, as user-defined uniaxial materials named CFSWSWP and CFSSSWP for wood and steel sheathed SWP, respectively. The proposed analytical models are validated using the experimental tests results obtained from the literature, where a good agreement has been achieved. In order to investigate the influence of the CFS SWP parameters variation on the hysteresis characteristics of the response, several non-linear quasi-static analyses have been carried out using different CFS SWP configurations. The key parameters which have most affected the cyclic response were identified and assessed.

Effect of seismic degradation on the fragility of reinforced concrete bridges

In seismic regions, structures are likely to experience multiple seismic events during their service lives. As a result, the seismic reliability of structures may degrade from the design standard with each passing earthquake. Therefore, there is a need to investigate the effect of seismic degradation on the reliability of structures in subsequent earthquakes. In the existing literature, performance of RC structures under a sequence of earthquakes has received limited attention. More work is required to understand the effects of seismic degradation mechanisms in different structural systems.This paper investigates the seismic degradation of reinforced concrete (RC) highway bridges and the effect of degradation on the performance and reliability of bridges subject to future seismic events. In particular, the focus is on the degradation of bridge columns that are typically the primary lateral load resisting components in highway bridges. For this purpose, probabilistic models are developed to predict the effect of past earthquakes on the structural properties of RC bridge columns and their steel reinforcement. The proposed models are assessed using seismic degradation data generated through nonlinear time history analyses of RC bridges subject to ground motions obtained using detailed finite element (FE) models. The developed degradation models are then used to assess the effects of seismic degradation on the seismic vulnerability of an example RC highway bridge with one single-column bent. The results show that seismic degradation in RC columns can significantly increase the seismic vulnerability of RC highway bridges.

Material Study of a Short Seismic Link in a Dissipative Structure of a Vertical Industrial Boiler

Submitted paper presents brief information about structural dissipative design of a power plant boiler structure. The main attention is paid to the selection of material solution. Several material combinations of materials for dissipative members and other structural elements have been evaluated. As a measure of material combination effectiveness has been chosen a ratio between structural stiffness of primary and secondary lateral load resisting system. Probabilistic analysis of the structural sub-section has been carried-out for the most common material combination with steel S235 used for seismic links. Probabilistic analysis has been performed for the evaluation of the risk of material hardening in links and probabilistic distribution of material properties.

Seismic behavior of T‐shaped steel reinforced concrete shear walls in tall buildings under cyclic loading

SummaryShear walls are often used as the primary lateral load resisting elements in high‐rise buildings because of their large in‐plane stiffness and strength. It is a common practice to combine rectangular walls to form T‐shaped, I‐shaped and L‐shaped walls for functionality and esthetic reasons. Three relatively slender steel reinforced concrete (SRC) shear walls with T‐shaped cross‐sections were constructed and tested to failure under cyclic lateral loading. This research was conducted to assess the failure mechanism, hysteretic behavior, ductility and energy dissipating capacity of SRC T‐shaped walls under various axial load ratios. All the specimens exhibited a flexural mode characterized by crushing of the concrete and buckling of the steel at the free web boundary. The experimental results showed good hysteretic characteristics without pinching phenomena. The ductility coefficient varied from 2.3 to 4.1, and the deformation capability decreased with the increasing of axial load ratios. The stiffness, strength and ductility of T‐shaped walls are dependent upon the direction of the applied lateral loads. Higher stiffness and strength and lower ductility are achieved when the flange is in tension. The failure mechanism suggested that special attention should be paid to the design of the free web boundary to prevent premature failure under compression. Copyright © 2014 John Wiley & Sons, Ltd.

Seismic Behavior of a Modern Concrete Coupled Wall

AbstractRC core walls are used commonly in modern building construction as the primary lateral load–resisting system. To meet architectural constraints, including elevator, stair, and doorway openings, common configurations include walls coupled together with heavily reinforced, low-aspect-ratio coupling beams. Numerous studies have focused on coupling beams and improved seismic performance and design of coupling beams. However, far fewer research programs have studied the seismic behavior of the coupled wall system. Coupled walls are typically used in mid- to high-rise construction, and understanding their seismic response requires simulation beyond the coupling beam and must include all important yielding components of the system. A research project was undertaken to investigate the response of a midrise coupled wall designed to meet current codes. The advanced testing capabilities of the University of Illinois at Urbana-Champaign George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES)...

Seismic Retrofitting of Steel Frames with Buckling Restrained Braces

Buckling-restrained braced frames (BRBFs) are used as primary lateral load resisting systems for buildings in high seismic areas. The main characteristics of buckling-restrained braces (BRBs) are enhanced energy dissipation potential, excellent ductility and nearly symmetrical hysteretic response in tension and compression. This paper presents an analytical study aimed to assess the feasibility of using BRBs as a retrofit scheme for existing steel frames. For that purpose, the seismic response of four two-dimensional frame models representative of typical steel frames was analyzed prior to and after including BRBs as a retrofit strategy. Comprehensive nonlinear static and time-history analysis were carried out for analyzing the frames. A set of seven code-compliant natural earthquake records was selected and employed to perform nonlinear time-history analysis. Frames were analyzed and designed based on 2800 Iranian Seismic Code. The evaluation was based on comparing seismic displacement demands such as target roof displacements, maximum displacements and inter-storey drifts. The results showed that the effectiveness of braced frames can vary significantly with ground motions, frame rises and retrofitting systems. It perceived that the seismic response of frames coincides well with the given design objectives.

Outrigger Structures for Twisted Tall Buildings

Employing twisted forms in tall buildings is a relatively new architectural phenomenon, as are the cases with the Chicago Spire and Shanghai Tower. These super-tall buildings employ outrigger structures as their primary lateral load resisting systems. This paper presents structural performance of outrigger structures employed for twisted towers. Twisted tall buildings of different twisted rates are designed with outrigger structures. Two cases are studied comparatively. The first case uses spirally slanted perimeter mega-columns in response to the twisted building form. The second case uses vertical mega-columns, set back from the building perimeter, and cantilevered floor slabs from the column lines. The comparative structural efficiency of these cases is presented.

Analytical and Experimental Lateral Load Behavior of Unbonded Posttensioned Precast Concrete Walls

The use of unbonded posttensioned (UPT) precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies. This paper introduces a design-oriented analytical model that uses simple formulae to estimate the nonlinear lateral load behavior of UPT walls, and compares this simple model with available experimental results. A previously developed UPT wall model based on fiber elements is also compared with experimental results. Each model is formulated to consider several critical limit states in the lateral load behavior of UPT walls. Comparisons showed generally good agreement between analytical and experimental results for three different test walls under monotonic and cyclic loading. The simple model is found to be sufficiently accurate for seismic design of UPT walls, and the fiber model is found to be sufficiently accurate for estimating UPT wall response under earthquake loading.