Monotonic Lateral Loading Research Articles

A new pile-soil interface and its application in battered mini piles under monotonic lateral load in cohesive soil

Numerical modelling of laterally loaded piles requires a robust pile-soil interface model. The conventional Coulomb friction model has limitations when predicting the soil-structure interaction at shallow depths for battered mini piles (BMPs) in cohesive (fine-grained) soils. This paper proposes an efficient pile-soil interface model to simulate laterally loaded BMPs in cohesive soils using three-dimensional finite element models (FEM). BMP systems have been commonly used to support lateral load-dominated lightweight superstructures. They are hybrid foundations with BMPs oriented at different inclinations and directions, mimicking tree root systems. FEM results indicate that the Coulomb model is unsuitable for simulating the pile-soil interface at shallow depth due to underprediction of shear resistance. The proposed interface model comprising a surface-to-surface cohesive damage interface with friction captures the lateral performance of BMPs accurately. The proposed model was implemented for a range of pile and soil properties to verify its suitability in understanding the behaviour of BMPs. The ultimate lateral capacity of BMPs increases with penetration length up to 1.5 m. While an increase in diameter and undrained shear strength increases the capacity, the lateral load eccentricity negatively impacts it. Interaction diagrams are developed to serve engineers estimate the ultimate lateral capacity of BMPs.

Seismic Performance of hollow section concrete-filled GFRP tubular columns under monotonic loads and cyclic loads

The experimental investigation and analytical reporting in this paper focus on the behavior of HS-CFGT members, specifically their response to both monotonic loads and cyclic loads. A total of 8 specimens, divided into two groups, each group with 2 kinds in loading type, including 6 columns under cyclic horizontal loads and 2 columns under monotonic lateral loads, were tested. The details of the experimental setups, procedures, significant observations encompassing failure modes, maximum bearing capacities, displacement corresponding to the peak load, load-displacement hysteretic curves, skeleton curves, stiffness degradation curves, and energy dissipation curves and were truthfully reported. The inspection of the experimental data has yielded several important conclusions regarding the effect of column parameters on the behavior of HS-CFGT columns. The most significant finding is that the influence of concrete strength and FRP tube thickness on the seismic performance of HS-CFGT columns is not independent of each other. Furthermore, the findings additionally suggest that HS-CFGT columns made of high-strength concrete demonstrate commendable ductility. The initial flexural stiffness for the preliminary design of HS-CFGT columns is also provided to facilitate the implementation of this innovative technology.

Experimental Investigations on Structural Behaviour of Reusable Interlocking Steel column base Connection with Demountability

Implementing a circular economy in construction is one of the potential approaches to limit the natural resource consumption by the construction industry and construction waste generation after demolition. There exist necessities for constructing buildings with easier demountability and direct reusability. One of the key aspects of reuse is designing with structural connections for demountability after service life, rendering the buildings for reuse. Therefore, this study endeavours to develop a directly reusable interlocking hold-down type column base connection for steel structures through full-scale experimental and theoretical investigations. The new reusable column base connection consists of a connector plate to replace the anchor rods in the traditional exposed column base connections to connect the concrete footing with the steel column and base plate assembly. This paper investigates the structural behaviour of the new reusable column base connection subjected to monotonic lateral loading and determines the effective embedment depth required for the connector to avoid concrete failure. A loading protocol that signifies reuse through repeated loading sequences is adopted for this study. Thus, each specimen is loaded for three repeated reuse cycles. A theoretical method based on the traditional component model concept representing the connection components as a combination of spring assembly is developed to predict the initial elastic stiffness of the connection. This will consequently aid in estimating the lateral displacement occurring for the corresponding design load. The theoretically predicted stiffness values are in good correlation with the experimental results. The design example for stiffness calculation is also provided for industrial practical applicability.

Macro-modelling of GFRG infilled RC frames incorporating pivot hysteretic model

GFRG (Glass Fibre Reinforced Gypsum) panels present a viable alternative to conventional masonry infills in masonry infilled RC frames. Based on the experimental study on the lateral load behaviour of GFRG infilled RC frames, it was understood that the GFRG panels enhance the structural performance of the RC framed structure. To delve further into this, numerical modelling of GFRG infilled RC frames with different fillings inside the cavities of the panel was performed using SAP2000. The GFRG panels were modelled using nonlinear layered shell elements, while the interface between the GFRG web and the infill material was represented using multilinear plastic link elements. The monotonic lateral load–deflection behaviour and the in-plane hysteresis response were simulated by performing monotonic and cyclic pushover analyses. The cyclic pushover analysis incorporated pivot hysteretic models for the materials, hinges and links. Validation of the proposed numerical models was carried out by comparing the results with those obtained from the experimental study. Key parameters such as peak load, initial stiffness, stiffness degradation, and energy dissipation were carefully compared to ensure the accuracy and reliability of the proposed model. It was observed that the proposed numerical model was able to capture the monotonic and cyclic load–deflection behaviour and other performance parameters. The numerical model accurately predicted the peak load in the positive direction but overestimated the corresponding value in the negative direction. Moreover, the overestimation observed in the cumulative energy dissipated for all the specimens is relatively minor and does not significantly affect the overall accuracy of the model.

Numerical modeling and failure analysis of caisson foundations subjected to the monotonic lateral loads

The caisson foundation has evolved into a suitable alternative foundation for offshore structures, specifically for offshore wind turbines (OWT). The OWT caisson foundations are exposed to a combination of lateral, vertical, and overturning moments. A precise assessment of horizontal load response is necessary to ensure the normal functioning of these foundations for a proper design. This paper presents the results of three-dimensional finite element analyses of the lateral load-bearing behavior of the caisson foundation used for offshore wind turbines. The numerical model was validated and cross-checked by experimental data from the literature. The caisson’s behavior and the soil response supporting the caisson foundation subjected to static horizontal loads were examined. The effect of the slenderness of the caisson foundation was examined by changing the diameter and the depth of the caisson. It was observed that the depth of a caisson has a more profound effect on the lateral load-bearing capacity of the foundation. The caisson’s rotation center or inflection point was found to be at a distance of approximately 0.8 times the caisson depth, and it shifted downward with the increase in caisson diameter. Soil upheaval in the loading direction was observed as a precursor to the pullout failure, which increased with loading eccentricity and decreased with the caisson depth.

An enhanced understanding of the lateral response of large-diameter monopile: Development of a new P-y curve

The present design practices of laterally loaded monopiles tends to discretize the pile into a series of beam elements and connect each element to uncoupled non-linear springs, or P-y curves, to represent soil reactions. The prevailing design codes tend to support the use of a universal P-y curve irrespective of pile configuration, flexural rigidity, and soil rigidity index. However, accumulating evidence suggests otherwise, underscoring the imperative to revise formulas, especially for large diameter rigid monopiles. This study conducts a thorough examination of load transfer and failure mechanisms in large diameter monopiles subjected to monotonic lateral loading in clayey soil. A refined formula is proposed to estimate ultimate net soil resistance, rectifying deficiencies in prevailing design codes prone to underestimation. Findings reveal significant influence of soil rigidity index on the P-y curve of rigid monopiles. Consequently, endeavours are undertaken to develop a new P-y formulation integrating the pivotal role of soil rigidity index. The newly devised P-y curve is anticipated to propel advancements in the design of large diameter monopiles, pivotal in offshore renewable energy exploitation.

Simulation of Preload Relaxation of Bolted Joint Structures under Transverse Loading

In this study, based on the Iwan model, the connection interface of the bolted joint structure subjected to lateral loads was simulated and comparatively analyzed. Commercial finite element software was used to model the bolted joint structure. Monotonic lateral loads and cyclic displacement loads were applied to the model. The changes in the preload force of the bolted connection structure, as well as the changes in the sticking zone and stress state of the connection interface, were analyzed, and the loading results of monotonic load and cyclic displacement load were compared. The results show that the contact interface stress decreases with the increase in displacement load, and this increase is also a nonlinear relationship, which is approximately in phase with the trend of the contact surface slip curve. The amount of contact surface stress loss and the amount of preload loss are not directly related to the magnitude of the initial preload, regardless of the loading conditions. The contact surface is also circular under any form of displacement loading, whether it is stressed or slipped. The amount of preload loss is proportional to the amount of bolt compression for that variable.

Behaviour of a laterally loaded rigid helical pile located on a sloping ground surface

Offshore wind turbines, crucial for electricity generation worldwide, face challenges from strong winds, waves, and uneven ocean floors. To address these issues while remaining cost-effective, an innovative foundation is essential. The study introduces a helical monopile with a circular helix made of the same material as the shaft, representing a significant advancement. The study employs both 1 g model experimental tests and numerical simulations (PLAXIS 3D) to explore how changing slope conditions, pile positions, and the inclusion of the helix affects the response under monotonic lateral loading. Factors studied include ground slope angles (flat, 1 V:5H, 1 V:3H, 1 V:2H, and 1 V:1H), pile positions along the slope (c = 0Dp, 2.5Dp, 5Dp, and 7.5Dp), and variations in the number and positions of the helix (Hp) (0.25Lp, 0.5Lp, and 0.75Lp). The investigation involved analyzing the spacing between helices about both the length of the pile (Lp) and the diameter of the helix (dh ). The eccentricity to the diameter of pile ratio (e/Dp) is maintained as 12. The main objective is to compare the effectiveness of large-diameter helical piles to conventional monopiles in resisting upward and lateral forces. Results show helical piles offer a 100% improvement in uplift resistance and a 53% increase in lateral resistance compared to monopiles. This significant enhancement in capacity, particularly on sloping surfaces where monopiles typically exhibit reduced performance, underscores the effectiveness of helical piles in enhancing lateral capacity compared to monopiles.

Predição da capacidade última de elementos em concreto armado usando metodologias de análises não linear

Abstract This work aims to investigate the ultimate capacity of reinforced concrete elements in terms of cracking and stiffness loss. Nonlinear finite element analysis (NLFEA) was performed in the ATENA software and compared with a proposed numerical simulation of nonlinear static analysis (NLSA), where material cracking is evaluated based on the loss of tangent stiffness of the elements. The analysis was applied to a low-rise reinforced concrete frame with constant axial loads in the columns, and monotonic lateral load applied at the top beam level. Both methodologies showed good agreement regarding the capacity curve and crack patterns, and the numerical simulation NLSA allowed the identification of the sequence of elements' stiffness loss. The results indicated a substantial similarity between the numerical simulation NLFEA and NLSA and the experimental test, indicating a high potential in predicting the nonlinear behavior of reinforced concrete.

An alternative p‐y method for piles in cohesive soils under monotonic lateral loading

AbstractPiles as onshore and offshore foundation structures are often horizontally loaded. The usual calculation method for the behaviour of piles under such loads is the p‐y method. For piles in cohesive soil, several p‐y methods are proposed in literature, leading in general to differing results. A finite element model dealing with the behaviour of horizontally loaded piles in clay soils was established and validated against field tests. Utilising the results of a vast number of numerical simulations, a new p‐y method was developed, which gives reasonable results over the entire range of possible loads for piles of almost arbitrary diameters and embedded lengths in clay soils of varying consistency. The method requires in total six soil parameters and accounts for the actual deflection of the pile and also the effect of pile tip shear resistance by iteratively adapted y‐multipliers which depend on the course of the deflection line and the distance of the considered point to the pile tip. The new method can be generally used for calculation of the bearing behaviour of piles in soft clay under monotonic loading and can serve as a reference for consideration of cyclic load effects or softening effects in stiff clays.

A practical framework for assessing the effect of cyclic softening of clays on the lateral response of single piles

Single pile foundation has been widely used for the most offshore wind turbines to resist the cyclic loading resulted from the wind and wave. The cyclic loading can result in the degradation of the shear strength and the stiffness of clays surrounding piles. This study proposed a practical framework for assessing the effect of cyclic softening of clays on the lateral response of piles. A 3D finite difference model was developed for the pile – soil interaction under cyclic loading and then verified by full-scale monotonic and cyclic lateral load tests conducted on the single pile in clay. The cyclic softening behavior of undrained clays was described by a nonlinear dynamic softening constitutive model developed by the authors. The effect of the loading type (i.e., one-way and two-way loading) and the loading amplitude on the cyclic lateral response of piles was investigated. Moreover, a prediction function was proposed and was demonstrated to be effective in estimating the evolution of cumulative peak lateral displacement of cyclically loaded single piles in clays. The proposed practical framework provides an alternative for predicting the cyclic response of single piles in clays based on the monotonic lateral load test of piles.

Multi-springs model for suction caisson under monotonic lateral loading

Suction caisson has been widely used as the foundation for the offshore wind turbines. The behaviors of suction caisson under lateral loading caused by the combined effects of wind, wave and current, are quite significant for engineering design. In this paper, a novel multi-springs model is proposed to estimate the foundation displacement behavior and soil resistance distribution under lateral loading. In the proposed model, the p-y and t-z springs are divided into multiple groups and their combined effect is considered to reflect the uneven distribution of interface normal stress outside the caisson. In this way, the enhancement and direction reversal of vertical friction resistance can be reflected, which is also validated by the centrifuge tests of suction caisson. Afterwards, the multi-springs model is adopted to study the static performance of suction caisson under monotonic lateral loading. It is found that the soil displacement field is gradually dominated by the caisson rotation, whose rotation centre moves upwards and stabilizes at about 0.7-0.8L. Compared to p-y and Q-z springs, t-z spring plays the key role in resisting the foundation overturning at the slightly rotation angle of caisson.

Simulation of complex triaxial tests with HySand, a new multisurface constitutive model in the hyperplastic framework

Offshore wind has a key role to play in the energy transition. The majority of offshore wind turbines (OWTs) are bottom-founded with monopiles [1]. Monopiles account for up to 35% of the installation cost of the OWT [2, 3]. Optimising the design of monopiles can thus lead to significant savings and increased competitiveness of OWTs in the energy market.
 The PISA project [4] has led to the optimisation of the design under monotonic lateral loading of monopiles founded in sands, clays, and layered profiles [5 ,6, 7]. Because of this optimisation, along with the increasing size of OWTs, and the deeper waters where they are installed, design under cyclic loading is becoming crucial. There are, however, significant shortcomings in current design methods to predict the effects of cyclic loading on a monopile: accumulated rotation, changes in stiffness, energy dissipation and strength.
 The PICASO project, a joint research project between the University of Oxford and Ørsted, seeks to develop a new design method for monopiles under cyclic loading in sands and clays. Similarly to PISA [8,9], this design method will use the finite element method to simulate the behaviour of monopiles. For PICASO, such simulation requires constitutive models able to capture the behaviour of soil under cyclic loading. However, available advanced constitutive models for sand face severe limitations [10, 11] and are not satisfactory for the simulation of cyclic loading.
 HySand [12, 13], a family of models developed in the hyperplastic framework, fills this gap. HySand_base is a 14 parameter multisurface plasticity model with non-linear elasticity, shear plasticity and hardening, and two plastic volumetric mechanisms resulting in non-associative plasticity: one dilation mechanism which value depends on the evolving density and anisotropy of the sample, and one density dependent consolidation mechanism.
 This document presents comparisons between the database on Karlsruhe fine sand by Wichtmann [14] and results of simulations with HySand_base. The focus will be on complex tests that other models fail to simulate adequately, such as undrained strain-controlled cyclic tests. Data and simulation with HySand_base of such test on medium dense sand are presented in Figure 1.
 HySand_base performs well across densities and types of triaxial tests. This gives confidence in its existing three-dimensional implementation in finite element codes, and demonstrates its value to future design processes.

Seismic Performance of L-Shaped RC Shear Walls of Buildings Subjected to Monotonic Lateral Loading

Seismic Performance of L-Shaped RC Shear Walls of Buildings Subjected to Monotonic Lateral Loading

Parametric study on lateral behavior of totally precast RC shear wall with horizontal bolted connection

Dry-type connections have gained considerable popularity worldwide due to their superior construction efficiency and quality. However, a significant drawback of most conventional dry-type connections is the direct embedding of connectors in the concrete wall panel, consequently causing stress concentration in the connections and leading to extensive spalling of concrete. This study introduces an innovative high-strength bolted connection as a solution to address the problem of stress concentration in concrete. To evaluate the seismic performance of the high-strength bolted connection, monotonic lateral loading tests were conducted. In this study, a finite element (FE) model was developed using ABAQUS software, and validated through experimental results. Furthermore, a parametric study was conducted using the FE model to assess the influence of several key design parameters on the lateral response and anti-slip capacity of the bolted connection in the precast shear wall. These parameters include bolt specifications, anti-slip coefficient, flange thickness of the H-connector, widths of the initial gap, axial compression ratio, and connection arrangement. The results indicate that the anti-slip capacity is not significantly influenced by the flange thickness of H-connectors and initial gap width, but it increases with an increase in bolt specification, slip coefficient, and axial compression ratio. Additionally, the ultimate bearing capacity of the precast shear wall remains unaffected by both the anti-slip coefficient and the initial gap width. Moreover, the high-stress area of the H-connector is concentrated at the ends. Finally, the design parameters are recommended according to the numerical analysis results.

Non-linear finite element modeling of damages in bridge piers subjected to lateral monotonic loading

Bridges are among the most vulnerable structures to earthquake damage. Most bridges are seismically inadequate due to outdated bridge design codes and poor construction methods in developing countries. Although expensive, experimental studies are useful in evaluating bridge piers. As an alternative, numerical tools are used to evaluate bridge piers, and many numerical techniques can be applied in this context. This study employs Abaqus/Explicit, a finite element program, to model bridge piers nonlinearly and validate the proposed computational method using experimental data. In the finite element program, a single bridge pier having a circular geometry that is being subjected to a monotonic lateral load is simulated. In order to depict damages, Concrete Damage Plasticity (CDP), a damage model based on plasticity, is adopted. Concrete crushing and tensile cracking are the primary failure mechanisms as per CDP. The CDP parameters are determined by employing modified Kent and Park model for concrete compressive behavior and an exponential relation for tension stiffening. The performance of the bridge pier is investigated using an existing evaluation criterion. The influence of the stress–strain relation, the compressive strength of concrete, and geometric configuration are taken into consideration during the parametric analysis. It has been observed that the stress–strain relation, concrete strength, and configuration all have a significant impact on the column response.

Centrifuge testing of improved monopile foundation for offshore wind turbines

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation designs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5–8 m and depths of penetration of 30–80 m. To limit monopile diameters and penetration depths, an improved monopile design: the ‘hybrid foundation’ comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the performance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments.

Effect of Lateral Reinforcement on Strength and Ductility of Reinforced Concrete Columns

Abstract: Concrete confined by stirrups has a greater ductility than unconfined concrete which is widely used in reinforced concrete (RC) structures and its behavior is a classic topic ofdiscussion. Non-linear behavior of reinforced concrete is complex due to involvement of various heterogenic material properties and cracking behavior of concrete. It is very important to understand the response and failures of columns subjected to lateral loadsin order to save lives and reduce the damage to the building components. ANSYS is widely used finite element analysis (FEA) software which has the tools to analyze structural elements and their non-linear behavior based on the finite element procedure The failure prediction of reinforced concrete elements is usually carried out using experimental testing, and the observations are recorded only at critical locations due to restriction at the cost of testing equipment and accessories. To avoid the destructive testing, cost-cutting of materials and labor, the behavior prediction of reinforcedconcrete elements is typically carried out using numerical methods like Finite Element Method which responds well to non-linear analysis as each component possesses different stress-strain behavior. In this study, reinforced concrete columns were modeled having different tranverse reinforcements and subjected to axial loads along with monotonic lateral loading, their behavior is studied in terms of deformation, stress, strain, crushing/cracking and forcedisplacement curves.

Effects of bond-slip on flexural behavior of reinforced nano-material modified UHPC beams: Experimental and numerical investigation

A series of central pull-out tests were carried out to assess the bond performance between steel bar and nano-material modified ultra-high performance concrete (nano-UHPC). The effects of parameters, such as the type of concrete and steel bar, the diameter of steel bar, bond length, the thickness of concrete cover, the length and content of steel fiber, and the nanomaterial type and content, on the failure mode and the bond stress-slip relationship were analyzed in detail. Subsequently, a constitutive model was proposed based on the experimental results for the precise prediction of the bond stress-slip relationship. Furthermore, to illustrate the effectiveness of the constitutive model, a reinforced nano-UHPC beam under the monotonic lateral loading was tested, and numerically simulated by a precise finite element model incorporating the constitutive model. Parametric studies were also conducted to evaluate the effect of critical parameters of the constitutive model on the flexural behavior of the reinforced nano-UHPC beam. The experimental results revealed that there was a superior bond performance between the steel bar and nano-UHPC. The increase in the bond length and the ribbed steel bar diameter were not conducive to the bond performance, and so did the decrease in the concrete cover thickness, steel fiber length and content. Nano-SiO2 and nano-CaCO3 had a positive impact, whereas nano-Al2O3 showed a negative effect. The numerical results indicated that both the bond strength and modulus had a significant effect on the flexural behavior of the reinforced nano-UHPC beam, whereas the slope of descending segment of the bond stress-slip relationship had an insignificant effect.

A macro‐element with bidirectional interaction for seismic analysis of unreinforced masonry walls

AbstractPrior to implementing retrofitting measures for seismic action, it is necessary to evaluate the global capacity of unreinforced masonry (URM) buildings. Even with simplified assumptions, equivalent frame (EF) modeling adequately captures global responses and failure mechanisms in existing buildings, making it a popular modeling strategy among structural engineers. However, macro‐elements employed in the EF modeling of URM walls consider in‐plane (IP) and out‐of‐plane (OP) behaviors separately by decoupling their interaction and require independent verification for OP failure involving limit analysis. Such decoupling of interaction is justifiable if proper wall‐wall/wall‐floor connections and rigid‐diaphragm action of slabs are ensured; however, OP failure is likely a result of inadequate connections. Multiple components of ground motion excitation and plan eccentricity in buildings can activate bidirectional interaction in such circumstances. Due to OP damage, the interaction reduces the full IP strength of a URM wall, resulting in overestimating its lateral capacity. This paper proposes a frame‐like 3D macro‐element incorporating the effect of OP action on the IP shear response of URM piers under static and monotonic lateral loads. Only two parameters modifying IP shear stiffness and capacity are required to account for the interaction. Analytical expressions for the interaction parameters are proposed from a detailed micro‐modeling study. The paper also demonstrates, within the EF modeling, the applicability of the proposed macro‐element for seismic analysis of regular URM shear walls with openings.