Uplift Load Research Articles

High Reynolds number aerodynamic testing of a roof with parapet

Aerodynamic testing was executed on a large-scale building with two distinct aspect ratios (1:6 and 1:3), at a large open-jet facility, Louisiana State University (LSU). To illustrate, a 1:15 scale test model was extensively investigated by experimental testing at a high Reynolds number (~2.3 × 107). The objective was to understand the performance of parapets in reducing the magnitude of localized and area-averaged roof pressures. Through analogy with bare-roof and several parapet configurations, the paper explores the performance of parapet walls and why they can be employed in aerodynamic mitigation. The results suggest installing a parapet wall will act as an aerodynamic mitigation device to reduce negative (uplift) loads. Large-scale testing indicates that the taller the parapet, the higher the reduction in mean and fluctuating pressures. However, depending on the roof’s aspect ratio, there is an optimal parapet height. The study concludes that 40–50% reductions in roof pressures can be achieved with parapets. Along the same lines, to yield high reductions in roof pressures, the parapet height is a key parameter. Short parapets may have low performance under conical vortices. The importance of the current study is that parapets, as well as other architectural features, are widely considered difficult to investigate by small-scale testing, at low Reynolds numbers, the leading cause of discrepancies between the laboratory and field measurements. Consequently, the current paper contributes to knowledge useful to explain the role of parapets in reducing aerodynamic pressures, for buildings to withstand wind loads at high Reynolds numbers.

Analytical and Experimental Study of Pile Capacity in Unsaturated Sandy Clay

The design of pile foundation in technical practice is based on saturated soil mechanic or empirical procedure that ignores the influence of matric suction. Understanding the pile behavior and predicting the capacity of pile in unsaturated soil are important topics in foundation design. An experimental model test has been conducted on a single concrete pile model with a diameter of 16 mm and L/d ratios of 6, 10, 15 and 20. Model pile has been driven into sandy clay in the test box and is subjected to compression and uplift loading. The tensiometer instrument has been used to measure matric suction and the SoilVision has been used to get an estimate of the entire Soil Water Characteristic Curve (SWCC). The shear strength of sandy clay has been examined using a series of unconsolidated undrained triaxial tests to identify the relationship between cohesion, internal friction angle, and matric suction. The result has shown that end bearing pile capacity, skin friction capacity and total capacity of single piles are significantly influenced by the contribution of matric suction. Based on the experimental result, end bearing capacity and skin friction capacity of pile in saturated soil equation have been modified to calculate total capacity of pile in unsaturated soils by considering the influence of matric suction.

Characterizing uplift load capacity of micropiles embedded in soil and rock considering inclined installation conditions

In this study, the uplift load-carrying behavior of inclined micropiles (MP) embedded in various soil-rock layer conditions was investigated. For this purpose, a series of model load tests and finite element analyses were performed. The focus was given on the effects of MP inclination angle (θ) and rock-embedded ratio (Zr/L). For MPs in rock, the uplift load capacity (Qu,θ) was highest when vertically installed and decreased with increasing θ. The Qu,θ of MPs embedded in soil-rock mixed layers increased with Zr/L and decreased with increasing θ. Marked increases in Qu,θ were observed for Zr/L larger than 0.6 for all θs. As MPs inclination increased, the load-carrying mechanism shifted from the frictional resistance towards the passive resistance. The MPs inclined configuration caused less mobilization of the frictional resistance within the rock-embedded zone while producing the passive resistance within the upper soil zone. This explained the reductions in Qu,θ with increasing θ for MPs with the rock-embedded condition.

Numerical Analysis of Geocell Reinforced Square Shallow Horizontal Plate Anchor

This paper presents the uplift behavior of horizontal square anchor in cohesionless soil reinforced with or without geocell in cohesionless soil using three dimensional analyses. The effects of embedded depth ( $$H$$ ), geocell width ( $$B_{g}$$ ), geocell height ( $$h$$ ), geocell pocket size ( $$a$$ ), distance from surface of plate anchor to bottom of geocell ( $$U$$ ), plate anchor width ( $$B$$ ), geocell material stiffness ( $$K$$ ), and relative density of cohesionless soil ( $$D_{r}$$ ) on the dimensionless breakout factor ( $$F_{q}$$ ) and uplift capacity of horizontal plate anchor ( $$Q_{ult}$$ ) were investigated numerically using PLAXIS 3D finite element software with Hardening Soil Model (HSM). The influence of these parameters on the dimensionless breakout factor was discussed and optimum design parameters ( $$B,\frac{{B_{g} }}{B},\frac{h}{B},\frac{a}{B},\frac{U}{B},K$$ ) were determined. Additionally, the results of three dimensional numerical analysis confirmed with those of laboratory indicate that the proposed model is able to capture the uplift load–displacement behavior of geocell reinforced square shallow horizontal plate anchor system in cohesionless soil.

Analytical Calculation of Critical Anchoring Length of Steel Bar and GFRP Antifloating Anchors in Rock Foundation

Antifloating anchors are widely used during the construction of slab foundations to prevent uplift. However, existing methods for calculating the critical length of these anchors have limited capabilities and therefore require further research. As the mechanisms which govern the displacement and stability of antifloating anchors are closely related to those of piles subject to uplift, a simplified anchor model has been developed based on existing concentric thin-walled cylinder shear transfer models used for pile design. Analytical expressions for the critical length of the steel bar and GFRP (glass fiber reinforced polymer) antifloating anchors in rock are derived accordingly before demonstrating the validity of the method through engineering examples. The research results show that when the length of an antifloating anchor is less than a critical length, shear slip failure occurs between the anchor and surrounding material due to excessive shear stress. When the length of an anchor approaches the critical length, the shear stress gradually decreases to the undisturbed state. If the anchor length is larger than the critical length, the uplift loads are safely transferred to the ground without causing failure. The ratio of elastic modulus between the anchor and rock mass was found to be positively correlated with the critical anchoring length. Because the elastic modulus of GFRP bars is lower than that of steel bars, the critical anchoring length of GFRP bars is greater than that of steel bars under the same anchor-to-rock modulus ratio (Ea/Es). The results show that the proposed calculation method for the critical length of antifloating anchors appears valid and could provide a theoretical basis for the design of antifloating anchors after further refinement.

Web–flange distortional buckling of partially restrained CFS beams under uplift loading

Cold-formed steel members are usually used as purlins in buildings to support roof cladding and thus they can be treated as beams restrained fully or partially in the lateral and torsional directions. However, when these beams are subjected to wind suction loading, their free flange is in compression, which may cause web–flange distortional buckling (WFDB). This paper presents an analytical study on the WFDB of zed-section purlins when subjected to uplift bending. A simplified model is proposed to describe the WFDB of partially restrained purlins, from which the formula for calculating the critical stress of the WFDB is derived. The present model is validated by the results obtained from the finite strip analysis.

Experimental Investigation of the Uplift and Lateral Bearing Capacity of Root Piles

The root pile, a new type of pile foundation with a variable cross-section, is introduced. The mechanism of root piles under uplift and lateral loading and the construction process are presented and discussed. The bearing capacity of root piles under uplift loading, lateral loading, and combined uplift and lateral loading was compared with that of conventional straight piles through field loading tests, which were performed on two straight piles and two root piles. The results indicate that the uplift and lateral bearing capacity of root piles is significantly greater than that of straight piles; the combined uplift and lateral loading has almost no influence on the uplift bearing capacity of single piles, but would weaken their lateral bearing capacity; the roots are engaged gradually from the top to the bottom under uplift loading; the resistance of the roots increased substantially because of the interaction between the soil and roots; however, the side friction of the pile shaft above the roots decreased because of this interaction. Increasing the burial depth of the roots could improve the performance of the roots for building applications.

Centrifuge modelling of rock-socketed drilled shafts under uplift load

Rock-socketed drilled shafts are widely used to transfer the heavy loads from the superstructure especially in mountainous area. Extensive research has been done on the behavior of rock-socketed drilled shafts under compressive load. However, little attention has been paid to uplift behavior of drilled shaft in rock, which govern the overall behavior of the foundation system. In this paper, a series of centrifuge tests have been performed to investigate the uplift response of rock-socketed drilled shafts. The pull-out tests of drilled shafts installed in layered rocks having various strengths were conducted. The load-displacement response, axial load distributions in the shaft and the unit skin friction distribution under pull-out loads were investigated. The effects of the strength of rock socket on the initial stiffness, ultimate capacity and mobilization of friction of the foundation, were also examined. The results indicated that characteristics of rock-socket has a significant influence on the uplift behavior of drilled shaft. Most of the applied uplift load were carried by socketed rock when the drilled shaft was installed in the sand over rock layer, whereas substantial load was carried by both upper and lower rock layers when the drilled shaft was completely socketed into layered rock. The pattern of mobilized shaft friction and point where the maximum unit shaft friction occurred were also found to be affected by the socket condition surrounding the drilled shaft.

Effect of Different Soil Saturation Conditions on The Ultimate Uplift Resistance of Helical Pile Model

Helical piles have many properties over the other types of piles systems include high tensile capabilities, the possibility of fast installation, applying load immediately after installation, and suitability for most soil's condition. In addition to that, helical piles have relatively less noise during installation; they represent a cost-effective alternative to conventional pile types. The use of helical piles grows in the world in the last fifty years. Many studies concentrate on the performance of this type of piles in fully saturated and dry soils. The achievement of the helical pile in unsaturated soils is rarely studied. So, to cover this small-scale demand model of the helical pile with double helices has been tested. Twenty tests were performed on three different models (pile with single helix, pile with double helices, and pile with triple helices) and pile shaft only, embedded in different conditions of soil saturation (fully saturated, partially saturated, and dry soils) under uplift loading. Three different matric suction of partial saturation were used of 6.5, 7.4, and 9.6 kPa. The results obtained from the tests showed that the highest value in the unsaturated soil was at suction 6.5 kPa compared to other soil saturation conditions. The results mention that model piles embedded in dry soil have lower values of ultimate uplift capacities. The increment in uplift resistance of additional helices of single double and triple helices than that of shaft pipe embedded within dry soil shows an increment by approximately about 170, 240, and 282% respectively, for fully saturation soil, the increment about 342, 463, and 585% respectively, and by about 400, 429, and 475% respectively for matric suction of 6.5 kPa.

Bearing capacity assessment of bored piles equipped with expander body systems using the mechanics of unsaturated soils

Bearing capacity of single piles are occasionally predicted using the renowned theoretical methods (α and β methods). These methods are based on laboratory tests, which can be time-consuming, but also applicable in foundation engineering practice for unsaturated soils. Full-scale pile load tests were carried out on bored piles equipped with Expander Body Systems in the Federal District of Brazil, known for its unsaturated, collapsible and porous soil. This paper has the aim to assess the applicability of the β method, considering the contribution of soil matric suction, in order to estimate the bearing capacity of these piles subjected to uplift and compression loads in unsaturated soils. Based on the experimental results, it is indicated that the use of the β method considering the matric suction, can be a useful tool for bearing capacity estimation of bored piles equipped with Expander Body Systems in unsaturated soils.

Wind resistance performance of a continuous welding stainless steel roof under static ultimate wind loading with testing and simulation methods

Ultrapure ferritic stainless steel provides a new generation of long-span metal roof systems with continuous welding technology, which exhibits many unknown behaviors during wind excitation. This study focuses on the wind-resistant capacity of a new continuous welding stainless steel roof (CWSSR) system. Full-scale testing on the welding joints and the CWSSR system is performed under uniaxial tension and static ultimate wind uplift loadings, respectively. A finite element model is developed with mesh refinement optimization and is further validated with the testing results, which provides a reliable way of investigating the parameter effect on the wind-induced structural responses, namely, the width and thickness of the roof sheeting and welding height. Research results show that the CWSSR system has predominant wind-resistant performance and can bear an ultimate wind uplift loading of 10.4 kPa without observable failures. The welding joints achieve equivalent mechanical behaviors as those of base material is produced with the current of 65 A. Independent structural responses can be found for the roof sheeting of the CWSSR system, and the maximum displacement appears at the middle of the roof sheeting, while the maximum stress appears at the connection supports between the roof sheeting with a significant stress concentration effect. The responses of the CWSSR system are greatly influenced by the width and thickness of the roof sheeting but are less influenced by the welding height.

Comparative study on compressive and uplift load tests of PHC pipe pile

There are 5∼8 m thick non self weight collapsible loess in the project site of a power plant. In order to study the bearing relationship between compressive and uplift piles in loess site, static load tests were carried out on PHC pipe piles with diameter of 400 mm and 500 mm and pile length of 12 m. Under the same pile top load, the displacement of uplift pile top is greater than that of compression pile top. Based on the measured load displacement curve, the uplift bearing capacity of PHC pipe pile with pile diameter of 500 mm is 32.5% higher than that of pile diameter of 400 mm. When the pile diameter is 400 mm and 500 mm respectively, the ultimate bearing capacity of PHC uplift pile is 26.24% and 27.70% of compression pile respectively. GM (1,1) model of grey system can fit and predict the load displacement curve of PHC pipe pile under compression and pull-out. Compared with the measured results,the relative error of GM (1,1) model of grey system is larger in the previous stages of load, and decreases gradually with the increase of load.

Responses of suction buckets subjected to sustained vertical uplift loads in sand

This study presents finite element analysis (FEA) results of suction buckets subjected to vertical sustained uplift loads, focusing on the suction pressure and the displacement responses. The accumulative seepage of water and the heave of the soil in the bucket are the key components of the displacement. The accumulative seepage of water is modelled using a layer of soft elastic material (water elements) beneath the bucket lid. The model is first used to investigate the suction pressure and the displacement responses under drained, partially drained, and undrained conditions. The components of the displacement are subsequently explained under different drained conditions. A critical uplift force is then defined when heave of the soil occurs. The influences of the key parameters on the displacement rates are analyzed. The fitting equations of the displacement rates with and without heave of the soil are presented, and the results calculated by equations are compared with those from available centrifuge tests and previous FEA.

Normally loaded inclined strip anchors in cohesionless soil

Plate anchors are among the most effective anchorage systems that are widely used to resist horizontal and inclined uplift loads in many offshore and onshore applications. Previous research on plate anchors has largely focused on the horizontal or vertical breakout problems, with limited attention directed towards obtaining a full characterization of the effects of anchor orientation angle. The present study utilizes displacement-based finite element analyses to investigate the stability and performance of strip anchor embedded in cohesionless soil for plate inclination angles ranging from 0° to 90° from horizontal, where the applied load is normal to and acts at the center of the plate. This study investigates the effects of scale and roughness, along with the geometry of the failure mechanism for various plate orientations and embedment depths. The analyses, presented in terms of a non-dimensional breakout factor Nq, show that the breakout factor increases significantly with an increase in the inclination, especially for angles greater than 45° in loose sand and greater than 60° in dense sand. The analyses also show that scale effects (anchor width) can affect capacity. Finite element analyses have been used to introduce simple design charts relating the breakout factor to the embedment depth and relative density. Comparisons to experimental and numerical studies showed good agreement.

Design parameters and behavior of helical piles in cohesive soils—A review

The emphasis of this review is to do a parametric analysis for the design of helical piles used in cohesive soils. Also, the enactment of helical piles’ behavior when placed in cohesive soils under various independent loading conditions like compression, uplift, and lateral loads has been discussed. Through a vast gathering of various literatures which is relevant to the design of helical piles, relations were obtained that would be ultimately valuable for future influences associated with the choosing of design parameters and behavioral studies on helical piles. In addition to design parameters, design methods were also considered and comparisons were made. Furthermore, attention is also sought from researchers on the need for further exploration of helical piles subjected to combined loadings and the significance of design parameters.

Experimental and Numerical Studies on Pull-out Behavior of Granular Anchor Pile Foundation Embedded in Sandy Soil

The granular anchor pile foundation (GAPF) is an improved foundation technique used to withstand compressive as well as tensile forces and effectively reduce the settlement of soil. In this paper, the behavior of a GAPF system was studied in sandy soil. Pull-out load tests were conducted on GAPF by varying different parameters viz. length of pile (250 mm, 350 mm and 450 mm), L/D ratio (7.5, 10 and 12.5) and group of piles (spacing 2D, 2.5D and 3D). The test results indicate that the pull-out capacity decreases with the increase in L/D ratio from 7.5 to 12.5. The group effect resulted in increased uplift load in comparison to that of a single GAP tested. Finite element analysis using PLAXIS 3D software had also been carried out to validate the results of physical model tests. On comparison of numerical and model study results, a reasonable agreement has been found.

Investigation on determining uplift capacity and failure mechanism of the pile groups in sand

Foundations of some structures such as transmission towers, mooring systems for ocean surface or submerged platforms, tall chimneys, jetty structures are subjected to uplift loading. In such cases, to increase the uplift resistance of piles, pile foundations like anchored piles, batter piles and micro piles are extensively employed depending on in-situ conditions. This paper deals with the contribution of pile surface to the uplift capacity and the failure mechanism obtained for the pile groups in sand, and the main goal of the study is to investigate the effect of the pile surface roughness on the uplift capacity for different spacing ratios between piles. Therefore, the paper presents some findings of a single pile and pile groups embedded in sand under uplift loading. The variables investigated include the pile surface, pile embedment ratio and the spacing ratio between piles. Experiments were conducted to study foregoing parameters, and three-dimensional analyses were performed using the finite element method to illustrate the failure mechanism of pile groups and the interaction between piles for different spacing ratios between piles. The results show that the finite element simulation results indicate good agreement with the experiment results, and all variables significantly affect the uplift capacity of piles.

Blast Vulnerability of Drop Ceilings in Roadway Tunnels

Tunnels are critical links within modern transportation networks and are susceptible to accidental explosion from vehicle fuel and cargo. They also present a target for terrorism due to unscreened public access. Roadway tunnels constructed with circular, oval, or horseshoe cross sections in the United States within the last 100 years have typically consisted of a road surface, tunnel liner, and drop ceiling. The tunnel liner was the main structural component that resists any over-tunnel loads as well as preventing substrate intrusion and cave-ins. The drop ceiling is hung from the liner and creates a plenum above the roadway for ventilation of vehicle exhaust as well as throughput for electrical conduits, utilities, fire alarms, and fire suppression systems. The typical design of a tunnel drop ceiling only considers gravity loading and forces exerted by pressure within the ventilation plenum—severe impulsive uplift loading from a blast on the roadway below therefore presents significant risk of ceiling panel damage or collapse. This study evaluates the likelihood of significant damage and collapse of tunnel drop ceilings under blast loading. Six scenarios consisting of three trinitrotoluene (TNT) equivalent charge sizes in two representative tunnels were analyzed using computational fluid dynamics (CFD) to generate blast demands on the drop ceiling, followed by a blast vulnerability assessment of the drop ceiling panel elements. Dynamic single-degree-of-freedom (SDOF) analyses were verified against finite-element (FE) solutions and used to evaluate the damage for a wide range of blast demands. The results indicate that modestly sized explosive hazards can induce significant damage to the drop ceiling, ranging from permanent deformation up to widespread collapse. Hardening options include flexural enhancement with fiber-reinforced polymer (FRP) as well as retrofit of the hangers. As an alternative, removing the ceiling and reconfiguring the ventilation system with modern jet fans can be a more cost-effective option for blast mitigation depending on the tunnel owner’s operational and/or financial constraints.

Uplift Behavior of Belled Piles Subjected to Static Loading

The uplift behavior of foundation is of great importance for the construction of foundations of ports, transmission towers and other structures that require to resist uplift loading. This research presents the results of several uplift static loading tests of prototypical belled piles. The load–displacement curve of belled piles is divided into three stages: initial linear segment, middle curve segment, and ending linear segment. The characteristic uplift capacities for the three stages are given by a graphics method. A bi-linear equation is given for predicting characteristic loading capacities of piles based on the ratio of bell to shaft diameters (bb/bs) and the embedment depth (L). Using the calibrated micro-parameters by the load–displacement curves, PFC2D is used to investigate the development of microcracks and formation of soil slip surface in the uplift test. The predicted uplift capacities by simulation can match the experimental value and estimated value by the suggested linear equation. The numerical result shows that the microcracks propagate, connect, and coalesce rapidly once the load–displacement curve reaches the middle curve segment. The final soil slip surface from numerical simulation varies with the geometric dimension of belled piles. The effect of bell to shaft diameters ratio (bb/bs) and embedment depth (L) on the uplift capacity is examined using numerical uplift tests. The result shows that uplift capacity of belled piles can be improved by increasing bell to shaft diameters ratio (bb/bs) and embedment depth (L).

Seismic Response of Multi Story Structure Strengthened with Micropiles

Micropiles are reinforced grouted piles that have small diameters commonly not higher than 30 cm. They are widely used for slope stabilization, controlling structural settlement, and in some cases, as retaining structures. Also, they are used for resisting dynamic uplift loads, seismic retrofit mainly in restrictive and low headroom areas, and retrofitting of historical monuments. The main goal of this research is to develop a finite element model that can capture the different aspects of seismic behavior of multi-story structure supported with deep foundation via using of micropiles. Also, a main target for the executing numerical modelling is to show the influence of the surrounding soil on this system and vice versa. Firstly, a representative two-dimensional finite element model is conducted to represent the soil-structure interaction system under seismic excitation supported with proper boundary conditions in PLAXIS 2D V20 for dynamic analysis based on previous recommendations considering the nonlinear soil behavior. The behavior of micropiles is studied and verified using previous results. Based on these models, the effect of lateral dynamic loads on the response of a structure with different foundation types is investigated. Also, a wide range of parametric studies, considering structure properties, earthquake magnitude, micropile diameter, micropile length, and the number of micropiles, have been carried out in order to investigate the actual interaction between soil, substructure, and superstructures. The study results showed that the seismic response of the structure is highly affected by the properties of the sub-surface soil layer. Consequently and similarly, analysis results established that underpinning using micropiles is an efficient technique for controlling the seismic response of existing structures.