Lateral Loading Conditions Research Articles

Nonlinear Frequency Veering in a Beam Resting on an Elastic Foundation

In this work we present an investigation into nonlinear frequency veering of an elastic Euler— Bernoulli beam resting on a Winkler elastic foundation subjected to a static lateral load and hinged—hinged, with a torsional spring at one end. The beam is assumed to have an initial quarter-sine shape rise owing to a constant differential edge settlement. The beam static deflection is obtained by using a combined numerical—analytical procedure that accounts for the induced nonlinear axial force to mid-plane stretching. The harmonic balance method is used to solve for the nonlinear natural frequency of the associated nonlinear temporal problem obtained using the assumed mode method. The results are presented in the form of characteristic curves which show variation of the nonlinear natural frequency of the three modes of a selected range of system parameters. These results indicate that, depending on the system parameters, the nonlinear natural frequency of various modes can exhibit complicated behaviors not found using linear analysis.

Studies on the behaviour of screw piles by the finite element method

A circular pile with helical blades is an old type of foundation, which has staged a comeback recently and is being used in a variety of situations. Most of the research on helical screw piles has been experimental or theoretical with the help of simplifying assumptions. The method of design adopted so far treats this pile as an annular plate, disregarding the intricacies of the geometry of the helix. It is only the versatility of the finite element method that can take into account the actual geometry of a spatial structure such as the helical blade at a microlevel. This is perhaps the first attempt at such an analysis to study the response of the helical screw pile within the elastic and nonlinear ranges. While the pile is linearly elastic, soil is considered both as a linear elastic medium and as an elastic–plastic medium following the Drucker–Prager constitutive model. Cases of smooth contact and frictional contact between soil and screw pile are also considered. Screw piles are studied under compressive, tensile, and lateral loading conditions. Moreover, their performance is compared with that of prismatic piles. A parametric study has also been attempted on some key geometrical features of the screw pile.

Analytical Behaviour of Bolt–Joint Intersection Under Lateral Loading Conditions

An analytical method is developed to provide a better understanding of bolt shearing across joint planes under lateral confinement. The study was undertaken in conjunction with a laboratory study of the double shearing of bolts in concrete. A review of various analytical methods is discussed, and the bending behaviour of the bolts is studied under both elastic and plastic conditions. Issues examined include; hinge point location, the effect of concrete strength on the bolt-bending behaviour; the influence of bolt axial loading and bolt diameter on the hinge point position with respect to sheared joint planes. It was found that the applied axial load on the bolt had a significant bearing on the location of the hinge points in different strength concrete, particularly at low strengths. The hinge point location is also influenced by the bolt diameter.

The Alternation of Peri-Implant Bone Response Exposed to Static Lateral Load

In the present study, peri-implant tissue alteration was studied histologically, and then differences in the gene expression pattern of certain proteins were analyzed using cDNA microarray analysis, under the influence of static lateral load. Beagle dogs were divided into two groups: control and load. Three months after the extraction of mandibular premolars, two implants were placed in each side of the mandible. Each group was further divided into subgroups for loading times of 1, 7 and 14 days. Immediately after the implant installation, a loading device was adhered between the abutments of neighboring implants. Afterward, the expansion screw of the load group was activated by 360-degree rotation, resulting in 0.7 mm horizontal expansion. After sacrificing the dogs, peri-implant tissue was collected, then microarray analysis for the detection of gene expression was performed, as well as histology. Histology indicated that the peri-implant tissue broke down under the influence of the load. Microarray analysis demonstrated the presence of load-sensitive gene expression even after 1 day. Differences in gene expression patterns in concert with static lateral load were demonstrated, even at an early stage post-operation. Further study may help in the diagnosis of pathological overload.

An assessment of impact strength of the mandible

In this study, an animal biomechanical study was performed to investigate the absorbed energy and impact strength of the mandible in relation to specimen position. Four regions of mandibles were loaded as complete pieces and gripped by the jaw of an Izod impact tester. All tests were carried out wet using the Izod impact test under two different impact loading directions, lateral and ventral. Absorbed energy and impact strength in kilojoules per square meter of specimen area were determined for each specimen. Under lateral impact loading, the absorbed energy was lowest for the anterior section due to the mental foramen's notch effect. The premolar region demonstrated more absorbed energy per unit area, or impact strength, than any other region. However, due to its small cross-sectional area, the premolar region also absorbs less impact energy. Under ventral impact loading conditions, anterior region absorbed twice as much impact energy than under lateral loading conditions. Premolar region absorbed the same impact energy under both lateral and ventral loading. Interestingly, mandibular angle under ventral loading absorbed five times more impact energy than under lateral loading. This behaviour is considered to be a mechanical adaptation to the actual loading of the mandible in vivo.

Modeling of Shear-Critical Reinforced Concrete Structures Repaired with Fiber-Reinforced Polymer Composites

This paper describes a study in which finite-element (FE) analysis procedures were used to predict the behavior of a reinforced concrete (RC) frame shear strengthened with fiber-reinforced polymer (FRP) composites. Details are presented of the numerical techniques used to represent the RC frame, the FRP, and the bond properties between the FRP and the concrete. The FE analysis is performed using a two-dimensional nonlinear FE analysis program based on the disturbed stress field model. To augment verification studies undertaken with beam specimens previously tested, a large-scale RC frame with one-span and two-story height was constructed and tested under lateral load conditions. The frame was first heavily damaged in shear, repaired with FRP wrap, and then subjected to a regime of reversed cyclic loads. A detailed comparison is carried out between analytical and experimental results for the hysteretic response, damage mode, crack pattern, and deformation of the frame. It is concluded that reasonably accurate simulations of the behavior of FRP-repaired shear-critical structures can be achieved through finite-element modeling.

Toe-Driven Tapered Fiber-Reinforced Polymer Self-Consolidating Concrete Composite Piles: New High-Performance Technology for Deep Foundations

Abstract Field experience shows that it has been often difficult to assure the structural integrity and uniformity of the cross-sectional area of cast-in-place concrete piles since cavities and soil pockets tend to form due to the lack of visibility and accessibility during construction. Moreover, corrosion in pre-stressed concrete, reinforced concrete, and steel shell piles has been very costly, exceeding $2 billion of annual repairs in the United States alone. This paper summarizes the findings of a comprehensive research program that was undertaken to develop novel technology that addresses both construction and durability related problems of piles. A new toe-driving technique was developed to install empty fiber-reinforced polymer (FRP) shells into dense soils. A specially developed cost-effective self-consolidating concrete (SCC), a material that flows under gravity and assures the integrity of piles is subsequently cast into the FRP tubes, which provide corrosion-resistant reinforcement. Driving tests were carried out on large-scale model FRP-SCC and steel piles installed in dense dry sand enclosed in a pressure chamber using the new technique along with conventional hammering at the pile head. FRP-sand interface characteristics were evaluated. The pile specimens were instrumented to investigate their dynamic behavior during driving, and their response to static compressive, uplift, and lateral loading. Both cylindrical and tapered FRP-SCC piles were tested. It is shown that the new toe-driving technique is very suitable for installing FRP and other thin-walled piles in dense soils. Results from dynamic pile driving and static load tests indicate that FRP-SCC composite piles are a very competitive and attractive option for deep foundation applications.

STUDY ON ASEISMIC SUSPENSION CEILING WITH STEEL FURRINGS

Collapse damages of suspended ceilings during recent severe earthquakes are focused as mentioned in references 3), 6). In order to establish aseismic design method of suspended ceiling, static lateral loading tests are conducted for both conventional and grid system ceilings that are partial models made of real components. Newly developed aseismic stiffeners are applied in the models and their availabilities are confirmed through the tests. Finally, evaluation formulas of buckling strength, which are based on Euler's formula, for combined bracing system are proposed.

Centrifuge Seismic Modeling of Pile-Supported Wharves

Abstract Five pile-supported wharf models were dynamically tested in a large-scale geotechnical centrifuge at UC Davis, California. Models representing pile-supported wharf configurations common in the United States were subjected to recorded acceleration time histories. Model variations included single-lift, multi-lift, and cut-slope rock dike configurations with foundation layers of loose liquefiable sand, marine clay, or dense sand, or a combination thereof. In addition, zones of soil were placed to model soil improvement. Structural elements representing pile-supported wharf geometries were placed within the models; some models included all vertical piles, while two of the models included batter piles. In addition, single piles were placed in two of the models and subjected to static cyclic lateral load tests. All models were extensively instrumented with nearly 100 instruments recording accelerations, pore pressures, linear deformations, and pile strains. This paper summarizes the design, construction, and testing of these complex models, and includes a brief summary of the results and recommendations for future modeling.

Influence of jig design on biomechanical evaluation of spinal construct stability

The biomechanical evaluation of spinal construct stability is of clinical importance as the results of such an evaluation provide information about the implant's performance in vivo in stabilizing the spine. The flexion/extension test is critical for the evaluation of spinal stability. However, it is more technically demanding to flex the spinal construct with the more structurally complex jig assembly than the assembly used in the compressive or twisting stability tests. A review of the literature shows that a variety of jig assemblies have been used to investigate the mechanical and kinematic behaviors of spinal constructs. However, there is little consensus about the influence of jig design on the investigated behaviors. The current study used the elastic beam‐column theory to predict the load and deformation of the spinal construct among four possible jig assemblies. The suitability of these four jig assemblies for the short‐ and long‐segment spinal construct was evaluated in detail with three indices: lateral deflection, loading condition, and failures at the bone‐screw interfaces. Among the four assemblies, the jig assembly that generates the distally increasing flexion moment and free cephalic motion was suitable for short‐segment fixation. The jig assembly that generates the constant flexion moment seemed to be more appropriate for long‐segmentation cases with physiologically acceptable deflection. This study aims to provide an insight into what jig‐related factors are associated with physiologically reliable outcomes of the flexion stability test for lumbar implants.

Rock socket piles at Mall of the Emirates, Dubai

The first snow centre in the Middle East, Ski Dubai, was constructed as part of the Mall of the Emirates retail and leisure complex in Dubai, United Arab Emirates. Opened in December 2005, the project comprises an 80 m high indoor ski slope and associated structures. The higher end of the slope spans over a three-level car park. The site is underlain by a variable sequence of very loose/loose silty sands, which in turn overlie solid geology comprising very weak/weak carbonate sandstone. It has been considered that the most appropriate foundation option to support the structure safely is a piled foundation. Bored and cast-in-place piles socketed into the rock were proposed. Detailed analyses of single piles and pile groups under axial and lateral loading conditions were undertaken. The seismicity and liquefaction potential were considered in the design in accordance with the requirements of Dubai Municipality. The preliminary test piles, which were carried out prior to the installation of the working piles, checked the pile capacity and load–settlement behaviour, confirmed the effectiveness of the piling technique used, and provided greater assurance of the satisfactory performance of the foundations. The results of the preliminary pile-testing programme were compared with those obtained from theoretical predictions based on the empirical relationships between pile capacity and the unconfined compressive strength. On the basis of this review, a guide for the design of rock socket piles in weak carbonate rocks suitable for use in Dubai is proposed.

Eficiencia de grupos de pilotes sometidos a carga lateral

This pa per in cludes a bib lio graph i cal re view of the o ret i cal and ex per i men tal be hav ior stud ies of piles sub jected to static lat eral load. The ex per i men tal be hav ior was ob tained from full scale load test and it pro vides a solid ba sis for com par i son with nu mer i cal meth ods of anal y sis, mainly beam on elas tic foun da tion, p-y curves method, and fi nite el e ments with lin ear mod el ing of soil. The com puter re sults were com pared with the ex per i men tal mea sure ments. The p-y curves method pro vides the best re sults, mod el ing ap pro pri ately the dis tri bu tion of lat eral loads and bend ing mo ments of piles in a group. The lin ear fi nite el e ment method mod els par tially the in ter ac tion soil-pile group and gives a rea son able an swer of the group ef fi ciency. The beam on elas tic foun da tion method gives re sults sim i lar to those us i ng the fi nite el e ment method and it im proves when non lin ear be hav ior of soil is con sid ered.

The behaviour of piles undergoing a change in lateral loading direction

Pile foundations installed for offshore applications or in earthquake prone areas must be designed to withstand transient static and cyclic lateral loads that may occur in different lateral directions at different times. Research has chiefly been devoted to studying the behaviour of a pile subjected to one dimensional lateral loading and the influence of changing the lateral direction of this loading has not been widely considered. This paper presents the results from a series of centrifuge tests which involve multi-stage loading of a pile, considering changes in loading direction. The behaviour of a pile subjected to an unload-reload loop in a single direction is compared to that of a pile reloaded at 90° to the initial loading direction. When piles are reloaded at 90°, the set of rules that apply to one dimensional reloading become ineffective because an ‘effect of recent loading history’ governs the behaviour. In particular, local hysteresis loops are widened and the global instantaneous stiffness varies. These experimental findings are in accord with predictions from a simple numerical model, which defines the soil surrounding a pile using a series of two­dimensional elastoplastic Winkler models along the pile length.

Earth Pressure on Caissons in Marine Clay Under Cyclic Loading

Coastal protection is proposed to be made out of a contiguous caisson type of wall. These caissons can be designed to resist both lateral static and cyclic loading. With adequate depth of embedment, the walls can be designed to offer significant lateral passive resistance to counteract the lateral static and cyclic loading arising out of wave action. This article describes a set of laboratory tests on model caissons embedded into soft marine clay with different embedment depths. Specially designed earth pressure cells are embedded into the caisson at different depths. A pneumatic system was used to apply lateral static and cyclic loading. Test beds were prepared conforming to soft clay conditions in a test tank of appropriate size. The test results reveal that with this type of arrangement the variation in earth pressure with depth can be conveniently established. The earth pressure developed is related to the lateral load applied. The depth at which the maximum earth pressure occurs is same for both static and cyclic loading. Further, under cyclic loading there is no failure encountered even under cyclic loading level corresponding to 0.9 times the ultimate static lateral capacity.

Interplay of cold working and nitrogen diffusion in austenitic stainless steel

For hardness measurements, the indentation depth is about 10% of the effective information depth under static loading. A change of the wear mechanism is observed under lateral loading conditions in oscillating ball-on-disc tests for nitrided austenitic stainless steel with an expanded austenite surface layer from abrasive to a subsurface plastic flow with a redistribution of the inserted nitrogen. This leads to an effective nitriding depth about 3–5 larger than the actual nitrided zone.

伝統木造建築における斗組の振動台実験

For the purpose of evaluating the seismic performance of masugumi, which is one of the most important architectural components in ancient Japanese wooden buildings, the shaking table tests using a full-size masugumi component were carried out. From the comparison of shaking table tests with static lateral loading tests, which had been carried out before, it was found that the initial stiffness obtained from shaking table tests was in agreement with the one obtained from static loading tests. In this paper, the rotating angle and slip deformation of each element of masugumi are also discussed.

Experimental tests and numerical analysis of a real RC structure upgraded by means of C-FRP

The paper presents results of the analysis of the lateral-load response of an existing RC structure seismically upgraded by means of C-FRP. The structure was tested “as-is” under monotonic lateral loading conditions. It failed by a column-type collapse mechanism. The structure was repaired and upgraded by means of C-FRP. The structure has been tested again by a cyclic load test. Results demonstrate the successful implementation of C-FRP with a significant improvement of stiffness, strength and lateral displacement capacity of the upgraded structure. Finally a numerical study has been started with the aim to correctly capture the experimental results.

An experimental study on static and dynamic bending behaviour of piles in soft clay

Static and dynamic lateral load tests were carried out on model aluminium single piles embedded in soft clay to study its bending behaviour. Model aluminium piles with length to diameter ratios of 10, 20, 30 and 40 were used. Static lateral load tests were conducted on piles by rope and pulley arrangement upto failure and load–deflection curves were obtained. Dynamic lateral load tests were carried out for different magnitudes of load ranging from 7 to 30 N at wide range of frequencies from 2 to 50 Hz. The load transferred to the pile, pile head displacement and the strain variation along the pile length were measured using a Data Acquisition System. Safe static lateral load capacity for all piles is interpreted from load–deflection curves. Dynamic characteristics of the soil–pile system were arrived from the acquired experimental data. The soil–pile system behaves predominantly in nonlinear fashion even at low frequency under dynamic load. The displacement amplitude under dynamic load is magnified by 4.5–6.5 times the static deflection for all piles embedded in soft clay. But, the peak magnification factor reduces with an increase in the magnitude of lateral load mainly because of increase of hysteretic damping at very soft consistency. The maximum BM occurs at the fundamental frequency of the soil–pile system. Even the lower part of the pile affects the pile head response to the inertial load applied at the pile head. The maximum dynamic BM is magnified by about 1.5 times the maximum static BM for model piles in tested consistency of clay. The maximum dynamic BM occurs at a depth of about 1.5 times the depth of maximum static BM for model piles, which indicates an increase of active pile length under dynamic load.

Cyclic Lateral Load Behavior of a Pile Cap and Backfill

A series of static cyclic lateral load tests were performed on a full-scale 4×3 pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap 5.18×3.05 m in plan and 1.12 m in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the ...

Porous Coated Motion Cervical Disc Replacement: A Biomechanical, Histomorphometric, and Biologic Wear Analysis in a Caprine Model

The biomechanical, histopathologic, and histomorphometric characteristics of cervical disc replacement were assessed in a caprine animal model. To investigate the biomechanical, porous ingrowth, and histopathologic characteristics of the Porous Coated Motion (PCM) Cervical Disc replacement (Cervitech, Inc., Rockaway, NJ). As an alternative to anterior cervical interbody arthrodesis, an artificial cervical disc serves to replace the symptomatic degenerated disc, restore the functional biomechanical properties of the motion segment, and preserve neurologic function. There were 12 mature Nubian goats divided into 2 groups based on postoperative survival periods of 6 (n = 6) and 12 months (n = 6). Using an anterior surgical approach, a complete discectomy was performed at the C3-C4, followed by implantation of the PCM device. Functional outcomes of the disc prosthesis were based on computerized tomography (CT), multidirectional flexibility testing, undecalcified histology, histomorphometric, and immunocytochemical analyses. There was no evidence of prosthesis loosening, or neurologic or vascular complications. CT showed the ability to image and assess the cervical spinal canal for the presence of compressive pathology in the area of the CoCrMo prosthesis. Multidirectional flexibility testing under axial rotation and lateral bending indicated no differences in the full range of intervertebral motion between the disc prosthesis and nonoperative controls (P > 0.05). Based on immunohistochemical and histologic analysis, there was no evidence of particulate debris, cytokines, or cellular apoptosis within the local or systemic tissues. Moreover, review of the spinal cord at the operative levels indicated no evidence of cord lesions, inflammatory reaction, wear particles, or significant pathologic changes in any treatment. Histomorphometric analysis at the metal-bone interface indicated the mean trabecular ingrowth of 40.5% +/- 24.4% and 58.65% +/- 28.04% for the 6 and 12-month treatments, respectively. To our knowledge, this serves as the first in vivo time-course study investigating the use of the PCM device for cervical arthroplasty. All 12 animals undergoing cervical disc replacement had no evidence of implant loosening, subluxation, or inflammatory reactions. PCM cervical arthroplasty permits unobstructed visualization of the spinal canal based on CT imaging. Segmental intervertebral motion was preserved under axial rotation and lateral bending loading conditions, while at the same time permitting porous osseointegration at the prosthesis-bone interface. Based on histopathologic review of all local and systemic tissues, there was no evidence of particulate wear debris, cytokines, cellular apoptosis, or significant pathologic changes in any treatment.