Extreme Lateral Loading Research Articles

Effect of Footing Shape on the Rocking Behavior of Shallow Foundations

Sources such as wind or severe seismic activity often exert extreme lateral loading onto the shallow foundations supporting high-rise structures such as bridge piers, buildings, shear walls, and wind turbine towers. Such loading conditions may cause the foundation to exhibit nonlinear responses such as uplift and bearing capacity mobilization of the supporting soil (i.e., rocking behavior). Previous numerical and experimental studies suggest that while such inelastic behaviors may engender residual deformations in the soil–foundation system, they offer potential benefits to the overall integrity of structures through dissipating energy and reducing inertia forces transmitted to the superstructure, thereby limiting seismic demand on structural elements. This study investigates the effect of footing shape on the rocking performance of shallow foundations in different subgrade densities and initial vertical factor of safety (FSv). To this end, a series of reduced-scale slow cyclic tests under 1 g condition were conducted using a single degree of freedom (SDOF) structure model. The performance of different footing shapes was studied in terms of moment capacity, recentering ratio, rocking stiffness, damping ratio, and settlement. For three foundations with different length-to-width ratios, the results indicate that increasing the safety factor and length-to-width ratio leads to thinner, S-shaped moment–rotation curves, mainly owing to the enhanced recentering capability and the P-δ effect. Moreover, across all foundation types, the repetition of a limited loading cycles with consistent rotation amplitude does not cause stiffness degradation or moment capacity reduction.

A hybrid inter-module connection for steel modular building systems with SMA and high-damping rubber components

The recent technological advancements achieved in modular construction have accelerated the trend of building taller self-standing steel modular building systems (MBSs), leading to a consensus among researchers regarding the vital role that inter-module connections (IMCs) play in the structural performance of MBSs subjected to extreme lateral loading. However, existing IMCs are typically designed such that the global structural system heavily relies on the hysteresis of the steel framing members, leading to severe sustained damage and costly, impractical retrofitting programmes. To unlock the full “disassembly and reuse” potential of steel MBSs, IMCs can be designed to contribute more effectively to the global damage distribution mechanism, by engaging specific “fuse” components which are easy to replace, improving the reuse prospects of volumetric modules. In this regard, the present study proposes a novel, hybrid IMC using custom corner fittings, a high-damping rubber (HDR) core and a shape-memory alloy (SMA) bolt. Calibrated and validated material models using data from experimental material characterisation tests have facilitated the full characterisation of the hybrid mechanical response, determining the deformation modes, stress states, hysteresis loops and mechanical parameters. The parametric FEA included the variation of bolt preload, endplate thickness, axial load magnitude and the vertical layout of the HDR core. The study represents a preliminary, proof-of-concept investigation, showcasing the favourable cyclic performance of the proposed IMC under the main deformation modes expected in tall self-standing MBSs during lateral loading. Due to the effective contribution of each component to the combined hybrid response, the connection succeeds in preventing the formation of significant plastic damage in the MBS’s corner fittings to facilitate reusability of modules.

Flexural–Shear Performance of Lightweight Concrete Panels with High Insulation Capacity

With the increased interest in the inherent fire resistance of organic insulators, various precast concrete insulation panels have been developed. However, precast concrete insulation panels still have structural and fire resistance problems resulting from a low composite action and unclosed cross-sectional details. To improve composite action and fire resistance, this study proposes the closed cross-sectional details of insulator panels with lightweight aggregate concrete, insulation material, and wire mesh. The objective of this study is to examine the flexural–shear performance of precast lightweight concrete panels with closed cross-sectional details developed for exterior cladding with high insulation capacity. Six full-sized insulation panels were tested under two-point top loadings. The main investigated test parameters to vary the moment–shear ratio of the insulation panels were the amount of the shear reinforcement and shear span–effective depth ratio. Test results indicate that the insulation panels with moment–shear ratios of 2.60 or higher were governed by shear, indicating that the longitudinal bars remained in an elastic state until the peak load of the insulation panels was reached. Thus, an increase in the moment–shear ratio of the insulation panels led to more brittle failure characteristics. Meanwhile, the insulation panels governed by flexure exhibited plastic flow performance in the applied load–deflection curve and well-distributed cracks. In particular, the maximal flexural moments of insulation panels with moment–shear ratios of 0.75 or less were higher than those calculated from the equations specified in ACI 318-19, indicating that the composite action was fully exerted. Overall, the developed insulation panels with cross-sectional details must be designed to a have moment–shear ratio of 0.75 or less to fulfil the ductile response under extreme lateral loads and exert full composite action.

Assessment of Damage and Residual Load Capacity of the Normal and Retrofitted RC Columns against the Impact Loading

In the current study, the effect of the extreme lateral loading on the square and circular Reinforced Concrete (RC) columns with and without retrofitting was investigated. 3D finite element modeling of the columns and impact loading condition was performed using the ABAQUS/Explicit software. The data of a real scale blast test carried out in our previous study were used to verify the modeling accuracy. The effect of secondary moments due to axial load, different geometrical characteristics of the steel jacket, compressive strength of the concrete, and the longitudinal reinforcement on the explosive capacity of the column and its residual axial strength were studied. Results showed that the circular columns perform better under the sudden lateral pressure than equivalent square ones. Also, steel jacketing increased the explosive capacity of the column, which was more effective in the circular columns than the square ones. The results also indicated that steel jacketing with less buckling capacity had the least improvements on the column capacity. It was found that the effects of the initial axial force in the column were significant on its behavior under explosive loading condition, which should be taken into account in any modeling approaches. In general, the P-δ phenomenon had less effect on the circular columns than the square ones. Also, the use of a high-strength concrete and a higher percentage of longitudinal reinforcement further influenced the retrofitted columns than unretrofited (normal) ones, which was more evident in the circular columns in comparison with square columns.

Study on confined end-regions of RC walls under monotonic and cyclic loadings

A study was conducted to clarify the influence of reinforcement detailing, slenderness and loading type on the capacity, damages and failure modes of confined boundary regions of reinforced concrete (RC) cantilever walls. It was found that the tensile strain prior to compressive strain affected the performance of thin wall boundaries and may lead to different failure modes compared to compression load only. It was also found that dense transverse reinforcement detailing in thin confined boundaries did not improve their performance. Some design and detailing practices were evaluated to determine their accuracy in preventing global buckling and bar buckling under extreme lateral loading. Numerical model that take into account reinforcing bar buckling was proposed to simulate the behaviour of specimens tested under monotonic condition. The model could simulate the observed response with good accuracy.

Geo-structural nonlinear analysis of piles for infrastructure design

Pile foundations are utilized to support a variety of important infrastructure that are subjected to static and/or dynamic lateral loads due to lateral earth pressure, vessel impacts, traffic, waves, wind, and earthquakes. The pile lateral behavior under extreme lateral loading is governed by two main factors: the interaction between the pile and surrounding soil and the material inelasticity of the pile itself. This presentation covers the state of the art of modeling the nonlinear response of piles. In addition, it describes the recent development of an efficient and robust approach for the analysis of piles based on the beam on nonlinear Winkler (BNWF). In this work, a general cyclic BNWF model is developed to account for the important features of soil–pile-interaction problem including lateral load characteristics, soil cave-in, soil–pile side shear, gap formation, and strength and stiffness hardening/degradation. The inelastic behavior of pile material is also modeled effectively by implementing the advanced fiber technique. The capability of the developed model in predicting the response of piles under lateral static, cyclic and seismic loading is validated by comparing the computed results with experimental data.

Structural performance of hybrid multistorey buildings with massive timber-based floor elements loaded under extreme lateral loads

Structural performance of hybrid multistorey buildings with massive timber-based floor elements loaded under extreme lateral loads

Strengthening and Retrofitting Strategy for Masonry (New Build Construction in Indonesia)

In Indonesia, number of non-engineered structures have significantly been found which the houses were built by unskilled workers using masonry either unconfined or confined. The non-engineered housing units developed in urban region are also vulnerable to seismic hazard due to the use of low quality of material and constructions method. Those structures are not resistant to extreme lateral loads and their failure during an earthquake can lead to significant loss of life. This paper is concerned with the structural performance of Indonesian low-rise buildings made of masonry under lateral seismic load. Experimental testing of masonry has been carried out in Indonesia to establish the quality of materials and to provide material properties for numerical simulations. The results found that the strength of Indonesia-Bali clay brick masonry are below the minimum standard required for masonry structures built in seismic regions, being at least 50% lower than the requirement specified in British Standard and Eurocode-6 (BS EN 1996-1-1:2005). In general, structural tests under monotonic and cyclic loading have been conducted to determine the load-displacement capacity of local hand-made masonry wall panels in order to: (1) evaluate the performance of masonry structure, (2) investigate the dynamic behaviour of the structure, and (3) observe the effect of in-plane stiffness and ductility level. Detailed numerical models of the experimental specimens were simulated in Abaqus using three-dimensional solid elements. Cohesive elements were used to simulate the mortar behaviour, exhibiting cracking and the associated physical separation of the elements. A range of available material plasticity models were reviewed: Drucker-Prager, Crystalline Plasticity, and Cohesive Damage model. It was found that the combination of Crystalline Plasticity model for the brick unit and the Cohesive Damage model for the mortar is capable of simulating the experimental load-displacement behavour fairly accurately. The validated numerical models have been used to (1) predict the lateral load capacity, (2) determine the cracking load and patterns, (3) carry out a detailed parametric study by changing the geometric and material properties different to the experimental specimens. The numerical models were used to assess different strengthening measures such as using bamboo as reinforcement in the masonry walls which the performance of wall found to be better

Static and cyclic rocking on sand: centrifuge versus reduced-scale 1g experiments

Shallow foundations supporting bridge piers, building frames, shear walls and monuments are often subjected to extreme lateral loading such as wind in offshore environments, or strong seismic shaking. Under such loading conditions, foundations may experience a host of non-linear phenomena: sliding on and uplifting from the supporting soil or even soil failure in the form of development of ultimate bearing capacity mechanisms. This type of response is accompanied by residual settlement and rotation of the supported structural system. Nevertheless, inelastic foundation performance can provide potential benefits to the overall seismic integrity of the structure. Thanks to such non-linearities, energy dissipation at or below the foundation level may eventually limit the seismic demand on structural elements. Several theoretical and experimental studies have provided encouraging evidence to this effect. This paper has a dual objective: first, to study the behaviour of shallow foundations under vertical and lateral monotonic loading and under lateral slow cyclic loading of progressively increasing amplitude; second, to explore the differences in foundation response between reduced-scale 1g and centrifuge 50g model testing. Emphasis is placed on interpreting their discrepancies by unveiling the role of scale effects. The role of soil densification due to multiple loading cycles with uplifting is also highlighted.

Inelastic behaviour of composite members under combined bending and axial loading

This paper presents an account of the results of a series of tests on partially-encased composite steel/concrete beam–columns. The experimental inelastic behaviour of members is examined under idealised conditions representing extreme lateral loading in combination with co-existing axial gravity loads. Members with three different cross-sectional sizes, utilising Grade S460 steel, were employed in the tests. The specimens were tested under major- or minor-axis bending in conjunction with a constant level of axial loading. The experimental arrangement and test rig constructed for this purpose are described together with the material properties and details of the specimens. The main experimental results from tests carried out on ten composite models are presented and discussed. In addition to providing essential data for validating future analytical and design studies, the experimental results and observations enable a direct assessment of several important factors. Particular emphasis is placed on key parameters related to yield and ultimate capacity as well as on ductility and residual strength considerations.

Performance of Wood Shear Walls Sheathed with FRP-Reinforced OSB Panels

This study addresses the development and structural testing of a hybrid sheathing panel designed to improve the lateral resistance of light wood-frame shear walls. The panel consists of thin outer sheets of oriented-strand board (OSB) bonded to strips of fiber-reinforced polymer (FRP) that are sandwiched between the OSB panels at the edges. The FRP-reinforced panel material selection and fabrication are summarized. Monotonic and cyclic tests were conducted to assess the performance of single-connector sheathing-to-framing connections using both OSB and FRP-reinforced OSB. Twenty-four full-scale shear walls were tested under monotonic and cyclic racking loads to determine the benefits of FRP-reinforced OSB to wall lateral load resistance. For a 102 mm perimeter nail spacing, FRP-reinforced OSB-sheathed walls exhibited increases in peak capacity and energy dissipation under cyclic loading of 27 and 73%, respectively, compared to walls sheathed with conventional OSB. Based on these experimental results, FRP-reinforced OSB panels appear to have significant potential for increasing the energy dissipation capacity and lateral load resistance of wood-frame structures subjected to extreme lateral loads. However, their full utilization will require higher strengths for critical shear wall components such as tension ties and framing interconnections, as well as improvements in sheathing-to-framing fastener performance.

Inelastic Behavior of X‐Bracing in Plane Frames

A numerical procedure for determining the hysteretic behavior of axially loaded, pin‐ended bracing members is outlined. The relationships between axial loads and deformations are computed recognizing the different states corresponding to appropriate load‐displacement conditions covering both buckling and yielding. Accurate numerical representation of the hysteretic response curve of bracing members is confirmed. By incorporating bracing elements in representative elastic rigid‐jointed plane frames, the contribution of braces to lateral load resistance in seismic excitation conditions is examined using numerical integration techniques. The efficiency of bracing systems is demonstrated. Both the lateral displacements and the loads induced in the main frame are less than those in the equivalent unbraced structure. Accurate prediction of post‐elastic behavior of bracing members has significant practical application potential particularly in industrial structures where the concept of an initially stiff yet structurally efficient system capable of degrading under extreme lateral loading conditions to a more flexible, but still load resistant structure, is very attractive.