Experimental and Numerical Retrofitting of Confined Masonry Buildings with GFRP Under Lateral Cyclic Loading

Although wind energy capacity has increased significantly in the last few decades, the installed capacity of offshore wind turbine still lags far behind that of onshore wind turbines due to the installation and foundation cost. The aim of this research project has been to clarify the influence of combined vertical and lateral loads, lateral cyclic load, and scour erosion on monopile foundations, in order to achieve more realistic and cost beneficial solutions for offshore wind turbine foundations and thereby increase its competitiveness when compared with other energy sources. Monopiles are the most popular foundation system today for offshore wind turbines installed in shallow to medium water depths. These relatively light structures (low vertical load), need to resist substantial lateral and moment loads. There have been a dearth of studies conducted to investigate the influence of vertical load on the lateral response of these rigid monopiles and the few available have drawn contradictory conclusions. In addition the lateral and moment loading exerted on monopiles due to wind, wave, and water currents is cyclic in nature. This type of loading can lead to the accumulation of lateral displacement/rotation and possible degradation of soil resistance over time. This evolution of pile head displacement and the change in soil stiffness with increasing cycles of load is poorly understood. Cylindrical structures, like monopiles, founded in offshore regions are commonly subjected to scour erosion caused by flowing water and currents, which induces loss of soil support around the pile, reducing the lateral load capacity and causing increased pile displacement. As a result, the system dynamics of the structure might be adversely affected. The results of numerical models suggest that the shape of the scour hole affects the loss of pile lateral capacity, however, there is a shortage of experimental test data that measure this effect. More than 60 centrifuge tests which are categorized into three groups are presented in this thesis, which consider the interaction of combined vertical and lateral loads, lateral cyclic load and scour erosion on the behaviour of rigid monopiles. The tests have been performed in homogeneous dry Geba sand in order to mimic simplified drained offshore soil conditions.

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral capacity, ductility and energy dissipation capacity of single piles under seismic load were evaluated in detail. The lateral capacities and the energy dissipation capacity of piles in dense sand were much higher than in loose sand. When embedded in loose sand, the maximum lateral load and the maximum lateral displacement of piles increased as e/d increased. On the contrary, when embedded in dense sand, the maximum lateral load of piles decreased as e/d increased. Piles with a higher load eccentricity ratio experienced higher energy dissipation capacity than piles with e/d of 0 in both dense and loose sand. At a given level of displacement, piles with circular cross sections provided the best energy dissipation capacity in both loose and dense sand.

Masonry walls are non-structural elements that can increase the stiffness and strength of building structures subjected to lateral loads. Reinforced concrete (RC) wall systems are structural elements that have been developed to improve structural performance. Because the use of large amounts of cement in RC is not environmentally friendly, cement-free concrete called geopolymer concrete (GC) has been developed. Research on GC structural beam-column joints and slab joints has proven that GC fulfils the strength requirements for structural elements. However, previous studies have not addressed the performance of reinforced GC wall panels (WPs) under cyclic loads. Therefore, this study filled the gap with the novelty of investigating the performance of reinforced GC structural WPs subjected to cyclic lateral loads. Numerical analysis was used to determine the performance of GC-WPs in resisting cyclic lateral loads, and an aerated concrete wall panel (AC-WP) model was used for verification. The study investigated GC-WPs that were 1500 mm wide and 200 mm thick, varying in solidity such that one was entirely solid (GC-WP1) and two had square openings in horizontal and vertical configurations (GC-WP2 and GC-WP3, respectively). The cyclic loading history referenced FEMA 461. The analysis resulted in hysteretic curves, ductility ratios, and stress contours. GC-WP1 achieved the highest maximum lateral loads (73,994 kN and-67,225 kN) compared to the other GC-WP models, with a high ductility ratio of 14,681. Results show that GC has the potential for use in WPs to improve their resistance to lateral cyclic loads.

The behavior of laterally cyclic loaded piles is affected by the magnitude and number of cycles of cyclic lateral loads as well as loading method (1-way or 2-way loading). In this study, calibration chamber tests were carried out to investigate the effects of loading method of cyclic lateral loads on the behavior of piles driven into sand. Results of the chamber tests show that the permanent lateral displacement of 1-way cyclic loaded piles is developed in the same direction as the first loading, whereas that of 2-way cyclic loaded piles is developed in the reverse direction of the first loading. 1-way cyclic lateral loads cause a decrease of the ultimate lateral load capacity of piles, and 2-way cyclic lateral loads cause an increase of the ultimate lateral load capacity of piles. The change of ultimate lateral load capacity with loading method of cyclic lateral loads increases with increasing number of cycles. It is also observed that the 1-way cyclic loads generate greater maximum bending moment than 2-way cyclic loads for piles in cyclic loading step and generates smaller maximum bending moment for piles in the ultimate state. It can be attributed to the difference in compaction degree of the soil around the piles with loading method of cyclic lateral loads. In addition, it is founded that 1-way and 2-way cyclic lateral loads cause a decrease in the maximum bending moment of piles in the ultimate state compared with that of piles subjected to only monotonic loads.

As exploration moves into deeper water, offshore pipelines, generally laid on the seabed, are an increasingly significant component of offshore hydrocarbon developments. Seabed pipelines are mainly subjected to the wave loading, which causes vertical settlement of pipelines. In this study, the vertical settlement of seabed pipelines under lateral cyclic loading in normally consolidated clay is investigated through the large deformation finite element (LDFE) analysis with the Coupled Eulerian Lagrangian (CEL) technique. The effects of strain rate dependency of the undrained shear strength and soil remoulding are considered by adopting an extended Tresca clay model during lateral cyclic loadings. Firstly, the LDFE results are compared with centrifuge test results and published LDFE data, showing a good agreement. Then, a series of LDFE cases are conducted to investigate the effects of pipe weight, lateral load amplitude, soil sensitivity, and the initial trench depth on the accumulated vertical settlement of pipelines under lateral cyclic loading. The LDFE results show that the affected clay zone around the pipeline due to the lateral cyclic loading is highly remoulded, and the initial trench depth has a great effect on the accumulated vertical settlement of pipelines. With the increasing number of lateral load cycles, the accumulated vertical settlement of pipelines first increases and then decreases. A modified expression is proposed to estimate the ultimate vertical settlement of pipelines in clay.

Seismic behavior of concrete-encased steel cross-shaped columns

This study is concerned with evaluating the response of single pile subjected to cyclic horizontal uniaxial loading. Combination of lateral cyclic loading and constant vertical or lateral load in two-orthogonal directions is also studied. Moreover, the influence of one- and two-way loading, number of cycles and the intensity of constant load in conjunction with the cyclic lateral load is presented. The study is further continued by comparing the performance of long and short single pile embedded in clayey soil. A series of three-dimensional finite element models using ANSYS code are conducted to model three-dimensional transient analysis as well as the complicated soil pile interaction. In order to verify the validity numerical model, the numerical response is compared with reported results obtained by experimental cyclic load test performed on single pile penetrated in soft clay. Results show strong coupling between the two-orthogonal direction of lateral loading that decreases the lateral pile capacity. The interaction relation of biaxial loading with the factor b = 1.2 and 1.15 for one- and two-way loading respectively may well approximate the analysis results. The results of study are presented in terms of lateral cyclic capacities, pile head deflection, displacement profile and bending moment over the pile length.

Behaviour of rigid piles in marine clays under lateral cyclic loading

As a natural stone aggregate, resources are reducing at a high rate due to the large concrete use. For the search of substitute material for natural aggregates, in recent years coconut shells are used in the concrete field. Reinforced cement concrete (RCC) portal frames are a very common structural element and used for resisting lateral loads. In this research single bay, RCC portal frames made with coconut shell concrete (CSC) are tested under lateral load and cyclic push-pull load. The results are compared with frames made with conventional concrete (CC). Four prototype bare frames cast in that two frames made with CSC and two with CC. Behavior and characteristics like load capacity, deflection, crack formation, concrete strain, stiffness, and ductility are studied. It was found that under cyclic push-pull load CSC frames are comparable with CC frames rather than under lateral load. The amount of deflection and strains are observed in the CSC frame is comparatively more than in CC frames. Stiffness and ductility also observed more in CSC frames than CC frames.

Truss modeling of as-built and CFRP-repaired RC bridge columns subjected to combined cyclic lateral loading and torsion

Buckling behavior of sandwich pipe under external pressure and lateral load

This study evaluates the effectiveness of integrating Carbon Fiber Reinforced Polymer (CFRP) composites for improving the response of interior Beam-Column (B-C) connections under the combined effects of axial and lateral cyclic loads. Eighteen Reinforced Concrete (RC) B-C connection models were simulated using the nonlinear Finite Element Analysis (FEA) ANSYS software. The beam had a cross-sectional dimensions of 125 × 160 mm with a total length of 1600 mm, and the column cross-sectional dimensions were 125 × 150 mm with a total height of 1050 mm. Different parameters were taken into consideration in this study including: the configuration, orientation, length, and number of layers of CFRP sheets. The nonlinear FEA models were calibrated and reasonably validated based on experimental test results previously published in reputable journals. The response of the B-C connections was then evaluated in terms of mode of failure, stress contours, hysteretic loops, load-displacement envelopes, ultimate lateral load and corresponding drift displacement, and energy dissipation. The nonlinear FEA results showed that the used strengthening schemes of CFRP composites can significantly enhance the B-C connection performance leading to higher lateral load and drift capacities as well as energy dissipation. The effectiveness of the employed CFRP composite increased as the bonding area and number of CFRP sheet layers increased. The orientation angle of the CFRP sheets had had a considerable effect on the energy dissipation and minor effect on the ultimate lateral load and corresponding drift.

Analysis of cylindrical and rectangular bucket foundations subjected to vertical and lateral loads in sand using a three-dimensional displacement approach

The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.

Lateral response of monopile reinforced by cement-improved soil in clay to monotonic and cyclic loadings: Laboratory model test and theoretical investigation