Static Axial Compressive Load Research Articles

Research progress on freeze–thaw constitutive model of concrete based on damage mechanics

Abstract In cold areas, freeze–thaw damage seriously affects the long-term use and safe operation of concrete structures. The constitutive model is an important foundation for predicting deformation and strength characteristics of concrete materials and for the non-linear analysis of concrete structures. This study is based on the elaboration of methods for the constitutive model of damaged materials by using damage mechanics and others. This study focuses on the existing constitutive model results of concrete under the static axial compression load, dynamic load, and coupling environmental load, and analyzing the problems in existing studies. Research has shown that segmented models exhibit higher fitting accuracy of concrete freeze–thaw constitutive model under static axial compression loads. By defining coupled damage variables, it is possible to approach the actual freeze–thaw damage of concrete under environmental coupling, and attention should be paid to the differences or interactions between damage factors. In order to meet the actual engineering needs of high altitude and cold areas needs to expand the temperature range of freeze–thaw tests and consider the dynamic loads impact on concrete damage, the establishment of constitutive model of concrete under the actual freeze–thaw damage is the focus of frost-resistant durability research of hydraulic concrete in cold regions.

Nonlinear forced vibration of functionally graded hybrid three-phase nanocomposite toroidal shell segments reinforced by carbon nanotubes (CNTs) and graphene nanoplatelets (GPLs)

This study proposes a unique three-phase functionally graded (FG) hybrid nanocomposite material reinforcing the toroidal shell segments to investigate the nonlinear forced vibration using Reddy's higher-order shear deformation theory, von Karman geometrical nonlinearity and Stein-McElman's assumption along with the Hamilton principle. The examined toroidal shell's material consists of polymeric resin, carbon nanotubes (CNTs), and graphene platelets (GPLs) as nanocomposites. The material properties have been derived based on a modified Halpin-Tsai micromechanical model. Four distribution patterns have been studied: uniform (UD), FG-X, FG-O, and FG-V. The continuous distribution of GPLs and CNTs leads to inhomogeneous position-dependent properties throughout the shell thickness. The obtained differential equations of motion have been reduced to ordinary equations using Galerkin's technique. A multi-scales method (MSM) is used to estimate a closed-form solution representing the frequency-amplitude relation, and the state space representation is used along with numerical fourth-order Runge Kutta method (RK4) to obtain the nonlinear dynamic response of the toroidal shell. The accuracy of the current results obtained has been verified by comparing them with the relevant literature and numerical results using (RK4). In addition, the influence of both GPLs and CNTs weight fractions, nanofillers’ distribution types, longitudinal and circumferential wave numbers, elastic foundation parameters, static axial compression load, transverse excitation load, damping ratio, geometrical characteristics of the toroidal shell on the dimensionless natural frequency, nonlinear primary resonance (frequency-amplitude curve), and nonlinear dynamic response are carefully studied. The results found that combining (GPLs & CNTs) into the shell's matrix improves performance, especially in concave shells compared to convex ones. The FG-X pattern reduces peak resonance amplitude and improves natural frequency. A reduction of 12.3 % is observed for convex shells, and 21.5 % for concave shells compared to FG-O.

Experimental investigation of the damage characteristics and seismic response of moment-resisting bolted column base joints for precast concrete frames

Although several studies have been carried out on the development of bolted dry joints for precast concrete structures, damage assessment and seismic performance of bolted dry joints for column base joints under the different axial compression ratios have been rarely studied. In this study, six half-scale reinforced concrete columns, half of them were bolted connected and others were monotonically connected to the foundation, are subjected to combined cyclic lateral load and static axial compression load. The tests were carried out under three axial compression ratios: 0.10, 0.20, and 0.30. The seismic performances, including failure modes, lateral load-displacement responses, displacement ductilities, energy dissipation capacities, stiffness degradation behaviors, and moment-curvature responses, were evaluated and compared. The influence of axial compression ratio and reinforcement details on the seismic performance, plastic hinge characteristics, and damage assessment of specimens was also investigated in detail. The experiment results show that the increase of axial compression ratio from 0.1 to 0.3 increased the lateral load capacity, secant stiffness, and plastic hinge length while reducing the ductility. The efficiency of current formulations to predict plastic hinge length for the determination of plastic hinge length of specimens was also compared. Proposed damage descriptions for different performance levels (or damage states) were summarized and observed damage states correlated with drift ratio demands. Some modifications to the Park and Ang damage index for each damage state were proposed and stiffness reduction factors for the damage states were comparatively investigated. In addition, the displacement-based seismic capacities of this novel RC column base connection are presented in detail.

Biomechanical testing of canine tibiae: Changes resulting from different tibial tuberosity advancement techniques - Pilot study.

The objective of the present pilot study was to determine the force required to break (a) intact canine tibiae, (b) tibiae following the osteotomy of the tibial tuberosity and (c) tibiae following Tibial Tuberosity Advancement- (TTA-) rapid surgery. Six pairs of tibiae of dogs between 15 and 35 kg body weight were used in a cadaver study. Three groups were created with four tibiae in each group; intact (Group 1), osteotomy of the tibial tuberosity and tibial crest (Group 2) and TTA-rapid (Group 3). The tibiae were put under static axial compressive load, applied until failure. The force required to break the tibiae was termed maximal force (F max). The mean of F max was 8193.25 ± 2082.84 N in Group 1, 6868.58 ± 1950.44 N in Group 2 and 7169.71 ± 4450.39 N in Group 3. The sample size was small for a statistical analysis but as a preliminary result, we have determined the force (F max) required to break canine tibiae. Furthermore, we hypothesise that osteotomies result in weakening of the tibial structure.

Lateral Impact Response of Elliptical Hollow and Partially Concrete-Filled Cold-Formed Steel Columns Under Static Axial Compression Load

In recent years, the use of partially concrete-filled steel tubular (PCFST) columns has been considered due to their cost-effectiveness and reduction of structural weight in bridge piers and building columns. One of the critical discussions about these columns is their impact resistance. In this article, the dynamic response of hollow and PCFST columns with elliptical cross-section under simultaneous loading of static axial compressive load and lateral impact load is presented using finite element modeling in ABAQUS software (FEA). To ensure the accuracy of the numerical modeling, the analysis results are compared with the results of previous works. The effects of different parameters such as impact velocity, the height of the impact location, the impact direction, the impact block mass, the size and shape of the impact block are investigated in this paper. The results of the numerical analysis showed that the partially filled specimens had better performance than the hollow specimens. The changes in impact direction and impact block mass parameters have a significant effect on the failure of the columns, especially when they are under high impact velocity. Changing the impact velocity significantly affects the impact resistance of specimens. However, the size and shape of the impact block did not have a significant effect on the displacement of the column against the impact loading.

Behavior of Reinforced concrete Columns Strengthened Using CFRP Sheets under Sustained Loading (Dept.C)

This paper investigates experimentally the behavior of axially and laterally loaded square reinforced concrete columns wrapped with CFRP sheets with and without sustained loading. The experimental work includes twelve large scale square columns with CTOSS section 200x200 mm and 2500 mm height. The parameters to be investigated are the percentage of sustained loads (40% and 80% of the ultimate load), and the lateral loads (equivalent to 5% and 10% of the axial load). The columns are kept loaded, until being tested up to failure under static axial compressive load in addition to the different values of the lateral loads.

Full-Scale Load Testing of 75–90-m-Long Post-Grouted Drilled Shafts in Suzhou Stiff Clay

Abstract This article evaluates the effects of post-grouting on axial behavior of long drilled shafts in stiff clay. Static axial compression and tension load tests were conducted on four ungrouted and six post-grouted shafts to investigate the effects of post-grouting on axial capacity and load-transfer mechanism. After post-grouting, axial capacity increased more than 100 %. Prior to failure, the relationship between the normalized axial load Q/Qmax and shaft head displacement Δ/D was nonlinear for ungrouted shafts. Compared with cases presented in the literature, much greater shaft displacements were required to mobilize shaft tip resistance and skin resistance, indicating a softer load-displacement response. The contribution of tip resistance to the overall load capacity was small for both ungrouted and post-grouted shafts because of their length. Shaft load capacity was significantly underestimated by the standard penetration test (SPT)-based method and α-method and was more reasonably estimated by the β-method. The cone penetration test (CPT) direct method yielded generally reliable predictions of skin resistance mobilized in the upper stiff clay soils; however, this method significantly underestimated skin resistance in the underlying very stiff to hard clay layers. Considering uncertainties in current design methods, results of this study suggest that field load tests are needed prior to construction to obtain site-specific design parameters.

Crashworthiness characteristics of natural ramie/bio-epoxy composite tubes for energy absorption application

Using metallic materials in automotive structures increases weight, fuel consumption and cost, therefore, certain trends have begun to use lightweight and cheaper materials. Fibre composites are used in automotive applications because they are stiff, lightweight and stronger than bulk material, as well as they have a comparable energy-absorbing capacity to that of metallic materials. The aim of this study is to investigate the potentials in natural ramie/bio-epoxy composite in crash energy absorption applications. Cubic specimens consisted of 12, 24 and 30 plies of ramie/bio-epoxy laminates with 50, 80 and 120 mm long which were prepared by hand layup method. Static axial compression load was then applied and the energy-absorbing capability of the ramie/epoxy composite was evaluated. The crashworthiness characteristics of the composite tubes were evaluated by measuring the average and peak crushing load, specific energy absorption, total absorbed energy and crush force efficiency in quasi-static axial compression. The failure mode and behaviour of the tubes were investigated by taking photographs and recording the load–displacement curves during the test accomplishment. The test results indicated that natural ramie/bio-epoxy composite tube has the great potential to be used as an effective energy-absorbing device.

Investigation of Performance of Soil-Cement Pile in Support of Foundation Systems for High-Rise Buildings

This paper presents the experimental study of Soil-Cement Pile (SCpile) by wet mixing method in sandy soils, with the typical project at An Trung Complex apartment, Da Nang city, Vietnam. With the characteristic of soil layers is sandy soil, the strength of laboratory stabilized soils with the amount of cement from 150¸300 kg/m3 was determined. Simultaneously, the authors also performed the experiments of 20 test piles collected from the site which has cement content about 280 kg/m3 and the unconfined compressive strength qu= (4.5-6.0) MPa. After that, a full-scale model static axial compressive load tests of two single piles and a group of four piles with diameter 800 mm and 12 m length were also conducted. The experiment results show that the bearing capacity of every single pile is 1.200 kN with settlement 6.93 mm and the group of four CSpiles is 3.200 kN with settlement 5.03 mm. The results presented in the paper illustrate that SCpile is the suitable solution for foundation construction process with low cost and saving time for high rise buildings. The result shows a capable application of soil cement piles for support of high-rise buildings.

Experimental Investigation on Load Carrying Capacity of Micropiles in Soft Clay

Use of high capacity micropiles is in great demand today because of their ability to solve some typical foundation problem like the construction of low- to medium-rise buildings over a soft to the very soft clayey soil of large depth. The normal practice of construction of long cast-in-situ concrete piles is costly and time consuming for this type of soil. In the present study, the group behavior of cast-in-situ grouted micropiles in highly plastic clayey soil is investigated. The paper discusses the experimental observations on the behavior of micropile groups under static axial vertical compressive load. The micropiles were constructed in the clayey soil of very soft consistency in a test pit of size 2.0 m $$\times $$ 4.0 m $$\times $$ 3.0 m. Load-settlement behaviors of two different sets of micropile groups were studied. In one set, micropile caps were rested on the ground surface and in another set, they were constructed sufficiently above the ground surface. The variables involved in this study were diameter, length, number and spacing of micropiles in a group. The ultimate load carrying capacity of a micropile group and the group settlement under the safe load were determined from experimental observations. The group efficiency and the resistance offered by the micropile cap alone were also determined from the present study. It is observed that the load carrying capacity of a micropile group increases with the increase in diameter, length, number, and spacing of micropiles. A nonlinear equation is established from the experimental data to determine the ultimate load carrying capacity of a micropile group.

Several Conclusions from Standard Test Method for Piles Under Static Axial Compressive Load

Based on test constructed on steel pile on a container terminal, the writer introduces the test method for steel pile under static axial compressive load, and analysis the data received form the test. Inadditional, the writer also gives some advices on piles test under static axial compressive load.

Plugging effect of open-ended piles in sandy soil

This paper presents an experimental study of the plugging effect on the capacity of open-ended piles installed in sandy soil. Full-scale tests, including dynamic and static axial compression load tests, were carried out on three instrumented piles with different diameters (508.0, 711.2, and 914.4 mm). To measure the outer and inner shaft resistances acting on the piles, a double-walled system was utilized, with instrumented strain gauges on the outside and inside walls of the pile. The results of field tests show that the inner shaft resistance was mostly mobilized at the location between the pile tip and 18%–34% of the total plug length. It was found that the soil plugging in the lower portion has influence on the inner shaft resistance. In addition, it can be also demonstrated that the ratio of inner shaft resistance plus annulus load resistance to total resistance was decreased with increasing pile diameters. The results of these tests show that the relationship between the degree of plugging and pile diameter is clearly established. Direct observations of the soil plugs were made and used to quantify both the plug length ratio (PLR) and the incremental filling ratio (IFR). Based on this result, it was realized that the N value of the standard penetration test (SPT) is highly correlated with the IFR.

현장시험을 통한 개단말뚝의 폐색효과에 대한 연구

연구에서는 사질토 지반에서 개단말뚝의 지지력에 영향을 미치는 폐색효과를 조사하기 위하여 현장재하시험을 수행하였다. 현장재하시험은 직경이 다른 총 3본의 시험말뚝(508.0, 711.2, 914.4mm)을 제작하여 각각 동재하시험과 정재하시험을 실시하였다. 내주면마찰력과 외주면마찰력을 분리 측정하기 위하여 시험말뚝을 이중관으로 제작하였고, 외부말뚝의 안쪽과 내부말뚝의 바깥쪽 표면에 변형률계를 부착하였다. 정재하시험 결과, 내주면마찰력은 선단부로부터 총 관내토 길이의 약 18-34%의 부근에서 집중적으로 발생하였고, 이를 통해 말뚝 선단부근의 관내토가 내주면마찰력 발현에 큰 영향을 미치는 것을 알 수 있었다. 또한, 말뚝직경이 클수록 전체지지력에 대한 내주면마찰력과 순단면적의 선단지지력의 합의 비가 감소하는 것으로 나타났다. 그리고 말뚝의 폐색율을 정량화하기 위해 시험말뚝의 incremental filling ratio(IFR)를 측정하여 분석한 결과, SPT의 N값과 상관관계가 있는 것으로 나타났다. This paper presents an experimental study of the plugging effect on the capacity of open-ended piles installed in sandy soil. Full-scale tests, including dynamic and static axial-compression load tests, were carried out on three instrumented piles with different diameters (508.0, 711.2 and 914.4 mm). To measure the outer and inner shaft resistances acting on the piles, a double-walled system was utilized with instrumented strain gauges on the outside and inside walls of the pile. The results of field tests show that the inner shaft resistance was mostly mobilized at the location between the pile tip and 18-34% of the total plug length. It was found that the soil plugging in the lower portion has influence on the inner shaft resistance. In addition, it can be also demonstrated that the ratio of inner shaft resistance plus annulus load resistance to total resistance decreased with increasing pile diameters. The results of these tests show that the relationship between the degree of plugging and pile diameter is clearly established. Direct observations of the soil plugs were made and used to quantify both the plug length ratio (PLR) and the incremental filling ratio (IFR). Based on this result, it was found that the N value of the standard penetration test (SPT) is highly correlated with the IFR.

Closure to “Comprehensive Load Test on Prestressed Concrete Piles in Alluvial Clays and Marl in Savannah, Georgia” by Yong Tan and Guoming Lin

Tan and Lin are commended on presenting a detailed case history of the performance of prestressed concrete piles installed and tested for a liquefied natural gas (LNG) facility in Georgia, United States. The pile testing program was comprehensive and included high-strain dynamic tests, Statnamic tests, and static axial compression and reciprocal lateral load tests. To extract information about the mobilized skin friction (shaft resistance) from the tests, the authors made use of the readings of the strain gauges installed at various levels along the test piles. From the results, the authors concluded, among other findings, that “the potential degradation of pile concrete stiffness attributable to pile driving should be accounted for in pile capacity analysis” (p. 178), a point that this discusser also made in the paper by Lam and Jefferis (2011). However, in this discusser’s opinion, this study would benefit from a fuller discussion of the process involved in the derivation of the pile stiffness (Young’s modulus) values for the various load tests because the chosen values of this important parameter can have a significant effect on the accuracy of the interpretation. Specific discussion points are given subsequently.

Analysis of stressed Timoshenko beams on two parameter foundations

In the present work, the static and dynamic behaviors of a Timoshenko beam subjected to a static axial compression load and a dynamic lateral load resting on a two parameter foundation have been studied using Adomian Decomposition Method (ADM). After verifying the obtained expressions by comparing its results with those found in literature, it is used to calculate the critical loads in the static case, natural frequencies for free vibration and beam response in forced vibrations. Parametric study is conducted to investigate the influences of different beam and foundation parameters on the critical loads, the natural frequencies and the response of the beam.

Crashworthiness characteristics investigation of silk/epoxy composite square tubes

This research concentrates on the evaluation of crashworthiness characteristics of natural silk/epoxy composite square tubes energy-absorbers. Composite laminate specimens were subjected to static axial compression load and experimental evaluation of the energy absorption capability of silk/epoxy composite. Specimens were in the form of square cross-sections with the dimension of 80mm×80mm and a radius curvature of 5mm. The variables in the experiment were the length of the tubes built 50mm, 80mm and 120mm. Meanwhile, the thickness of the walls, consisting of laminates of silk/epoxy of 12, 24 and 30 plies, correspond to equivalent wall thickness of 1.7mm, 3.4mm and 4.2mm, respectively. The parameters measured were the total absorbed energy (Etotal), and the crash force efficiency (CFE). Etotal is the measure of the amount of energy that the structure can withstand without failure and thus is a measure of its strength, while CFE gives a quantitative indication of the mode of failure of the composites. The mode of failure was observed using photography.

Comprehensive Load Test on Prestressed Concrete Piles in Alluvial Clays and Marl in Savannah, Georgia

This paper introduces a comprehensive full-scale pile load test program on 457-mm (18-in.) square prestressed concrete (PSC) piles in Savannah, Georgia. The program consisted of pile driving analyzer testing during initial pile driving and restrikes, Statnamic tests, static axial compression load tests, and reciprocal lateral load tests. On the basis of the interpretation of the test data, some important findings were obtained: (1) the alluvial clays in Savannah can only provide very limited resistance; (2) the time-dependent pile capacity gain after pile driving (i.e., setup effect) was approximately proportional to the pile embedment length into the Marl formation; (3) the estimated equivalent static pile capacities from the Statnamic tests were comparable to those from the static axial load tests; (4) the Marl formation is a competent bearing stratum for piles; (5) the potential degradation of pile concrete stiffness caused by pile driving should be accounted for in pile capacity analysis; and (6) the piles exhibited stiffer response under the monotonic lateral loading condition than the cyclic lateral loading condition. Finally, predictions on both axial and lateral pile capacities, using the soil parameters derived from the instrumentation data and back-analysis of the pile load tests, were compared with the corresponding pile load test results. The comparisons demonstrate that in combination of the static-bearing capacity formulas and the LPILE program, the developed soil models can make reliable predictions on both the vertical and lateral behaviors of the PSC piles driven through the soft alluvial clays to end bearing in the Marl formation.

Shear Mode Growth and Threshold of Small Fatigue Cracks in SUJ2 Bearing Steel

The shear mode propagation and threshold behaviors of small, semi-elliptical fatigue cracks were investigated in the JIS-SUJ2 bearing steel. Fully-reversed torsional loading was combined with a static axial compressive load to obtain crack growth in the longitudinal direction of cylindrical specimens. Non-propagating cracks smaller than ≅1mm in size were obtained (i) by decreasing the stress amplitude in tests using notched specimens, and (ii) by using smooth specimens in constant stress amplitude tests. The Mode II and Mode III threshold stress intensity factor ranges, ΔKIIth and ΔKIIIth, were estimated from the shapes and dimensions of non-propagating cracks. The threshold values decreased with a decrease in crack size, and there was no significant difference between ΔKIIth and ΔKIIIth. Wear on the crack faces was inferred by a powder and also by changes in microstructure in the wake of a crack. The ΔKIIth in the absence of interference of crack faces was estimated to be approximately 13MPa·m1/2 for a 1mm long crack.

クリープ沈下の影響を除いた杭の鉛直ばねの評価(構造)

The values of vertical stiffness of piles using for the monolithic analysis of a building and its foundation to estimate the earthquake-resistant performance are usually lead from load-displacement relationships of static axial compressive or pile-toe load tests. This procedure is not proper for such an extreme short-period load as earthquakes, and it is necessary to exclude creep from the test results. Applied the same method proposed by Tominaga (2004) for lateral load tests, it is found that the average ratio of the value of vertical stiffness excluded creep compared with the value involved creep is approximately 1.92.

On the natural frequencies of helical compression springs

The linearized disturbance equations governing the resonant frequencies of a helical spring subjected to a static axial compressive load are solved numerically using the transfer matrix method for clamped ends and circular cross-section to produce frequency design charts. The effect of varying the number of turns of the spring is investigated, and in the limit of large numbers of turns, our results validate earlier work on the vibration of helical compression springs in which the helix was modeled as an elastic beam with rigidities corresponding to those of unclosed circular rings.