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1.
Sara Heidarie Golafzani Abolfazl Eslami 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(3):216-230
ABSTRACT Since piles are one of the major geotechnical foundation systems, estimation of their axial bearing capacity is of great importance. Employing different design methods, resulting in a wide range of bearing capacity estimations, complicates the selection of an appropriate design scheme and confirms the existence of model error along with the inherent soil variability in bearing capacity prediction. This paper tends to evaluate different predictive methods in Reliability-Based Design (RBD) framework. In this regard, different static analyses, SPT and CPT-based methods are considered to evaluate which approaches collectively and which method individually, have more reliable predictions for compiled data bank. In order to assess reliability indices and resistance factors, two approaches have been considered, i.e. First Order Second Moment method (FOSM) and First Order Reliability Method (FORM). To investigate the reliability indices for different methods in both RBD approaches, various safety factors and loading ratios have been considered. Also, the Load and Resistance Factor Design (LRFD) resistance factors are calibrated for different target reliability indices and loading ratios. Results show that CPT-based methods are more reliable among other methods. Furthermore, the estimated efficiency ratio, i.e. the ratio of resistance factor to resistance bias factor, confirms this agreement. 相似文献
2.
《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3-4):218-228
This paper reports the results of load and resistance factor design (LRFD) calibration for pullout and yield limit states for steel grid reinforced soil walls owing to soil self-weight loading plus permanent uniform surcharge. The calibration method uses bias statistics to account for prediction accuracy of the underlying deterministic models for reinforcement load, pullout capacity and yield strength of the steel grids, and random variability in input parameters. A new revised pullout design model is proposed to improve pullout resistance prediction accuracy and to remove hidden dependency with calculated pullout resistance values. Load and resistance factors are proposed that give a uniform probability of failure of 1% for both pullout and yield limit states. The approach adopted in this paper has application to a wide variety of other reinforced soil wall technologies. 相似文献
3.
Masahiro Takenobu Masafumi Miyata Yu Otake Takehiko Sato 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):195-204
ABSTRACTThe Partial Factor Method (PFM) based on the Level 1 reliability design method was introduced in 2007 to the Technical Standards for Port and Harbour Facilities (TSPHF-2007) in Japan. After nearly 10 years of practical use of TSPHF-2007, the design standard has been revised based on requests from the practitioners who recommend the transition from the PFM to the Load Resistance Factor Design (LRFD). In this paper, we discuss the setting method of the target failure probability to determine the partial factors based on code calibration. Furthermore, we examine the impacts of implementing the LRFD concept to the TSPHF by taking the sliding and overturning of a gravity type quay wall as an example to represent port and harbour facilities. We found no practical difference in caisson width derived using the LRFD and the PFM, whereas the degree of matching of the target failure probability was somewhat more precise for the PFM. This finding indicates that the LRFD is a more reasonable design method than the PFM in terms of the simplicity of the performance function itself and the ease of engineering interpretation during the design procedure. 相似文献
4.
Naresh C. Samtani John M. Kulicki 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(3):231-243
ABSTRACT In the bridge design specifications of the American Association of State Highway and Transportation Officials (AASHTO) using the Load and Resistance Factor Design (LRFD) method, the loads and resulting force effects are given two-letter designations, e.g. “SE” for “force effects due to settlement”. The SE load factor is used to develop factored values of the induced force effects such as moments and shears in a bridge structure due to foundation movements. In 2018 AASHTO committees voted to adopt calibrated values of the SE load factors that account for the uncertainty in predicted foundation movements from different analytical methods. However, additional uncertainty can occur in the differential settlements. This paper explores the additional uncertainty in differential settlements of bridge foundations and retaining walls using the datasets for two analytical methods that were used by AASHTO to develop the SE load factors for foundation settlement. Normalised probability exceedance charts (NPECs), that integrate the concept of reliability index and data correlation, have been developed and their application in bridge and wall design process is discussed for a variety of scenarios. Guidance is provided for the practical implementation of differential settlement in bridge analysis through an example problem. 相似文献
5.
This paper presents a framework for calculating the resistance factors of load and resistance factor design (LRFD) for axially-loaded driven piles in clays that can fully account for all necessary reliability-related parameters. The Imperial College Pile (ICP) design method was adopted to determine the resistance factors. The ICP design method was selected because it has been widely verified and has produced close matches to measured pile load capacities. A high-quality database, originally employed to develop the ICP design method, was used to assess the uncertainties of base and shaft capacities. The uncertainties of dead and live loads were determined from previously reported results. The challenge of this paper was to identify the effect of base-to-shaft capacity ratios on resistance factors, which has not been considered in previous methodologies. The resistance factors, compatible with the load factors given in the American Association of State Highway and Transportation Officials (AASHTO) LRFD design specifications and those provided in the American Petroleum Institute (API) LRFD recommended practice, were calculated and proposed for different levels of target reliability index. The effect of base-to-shaft capacity ratios on resistance factors was noticeable, while the effect of dead-to-live load ratios on resistance factors was relatively small. 相似文献
6.
The resistance factor for pile foundations in load and resistance factor design (LRFD) is traditionally calibrated considering target reliability index (βT) and statistics of load and resistance bias factors. However, the resistance bias factor is hard to quantify statistically. Consequently, the design obtained using the calibrated resistance factor can still miss βT if the variation in resistance bias factor has been underestimated. In this paper, we propose a new resistance factor calibration approach to address this dilemma by considering “feasibility robustness” of design in the calibration process. Herein, the feasibility robustness is defined as a probability that the βT requirement can still be satisfied even in the presence of uncertainty or variation in the computed bearing capacity. For illustration, LRFD approach for pile foundations commonly used in Shanghai, China is examined. Emphasis is placed on re-calibration of resistance factors at various feasibility robustness levels, with due consideration of the variation in the resistance bias factor. A case study is presented to illustrate the use of the re-calibrated resistance factors. The results show that the feasibility robustness is gained at the expense of cost efficiency; in other words, the two objectives are conflicting. To aid in the design decision-making, an optimal feasibility robustness level and corresponding resistance factors are suggested in the absence of a designer’s preference. 相似文献
7.
Pile driving formulas, which directly relate the pile set resulting from a hammer blow to the static load capacity of the pile, are often used to decide whether a pile will have the required design capacity. However, existing formulas do not consider soil or pile type, and do not, in general, reliably predict pile capacity. In this paper, an advanced model for dynamic pile driving analysis was used to develop accurate pile driving formulas. The proposed driving formulas are validated through well-documented case histories. Comparisons of predictions from the proposed formulas with results from static and dynamic load tests show that they produce reasonably accurate predictions of pile capacity based on pile set observations. 相似文献
8.
依据上海地区某超高层商业建筑试桩的高吨位竖向抗压静载试验结果,通过对基桩的竖向极限承载力性状、桩身轴力传递特性以及桩侧阻力、桩端阻力发挥特性的分析研究,揭示了桩底注浆对基桩承载性状的影响情况,深入探讨了上海软土地区大直径超长后注浆灌注桩的荷载传递机理和竖向承载性状,提出了单桩承载力的估算方法。 相似文献
9.
The increase of pile resistance with time is referred to as ‘set-up’. This behaviour of driven piles has been widely discussed in many studies by researchers. Meanwhile, there has been little, if any, information regarding this aspect for drilled shafts. Performing a bearing capacity test for a shaft over time, however, requires higher costs and more complicated rigs compared to a driven pile. A database including results from five Osterberg cell-tested drilled shafts conducted at two different stages is considered, from which the set-up effect is statistically analysed. The reliability-based analysis technique using Monte Carlo simulation (MCS) is used to develop separate resistance factors to account for different degrees of uncertainties associated with the predicted reference resistance and the predicted set-up resistance in the framework of the load and resistance factor design (LRFD) method. By incorporating set-up into design, shaft length or number of shafts can be reduced and economical design of drilled shafts can be achieved. 相似文献
10.
In this paper, a framework based on Bayesian theory and proof pile load test results was used to update resistance factors of axially loaded driven piles. Prior to implementation of the framework, resistance factors were calibrated based on the distribution of the measured-to-predicted pile ultimate bearing capacity using the results of static pile load tests conducted to failure. These resistance factors and the distribution were considered to be “prior.” The prior distribution of the measured-to-predicted ultimate bearing capacity was updated based on Bayesian theory to incorporate additional proof pile load test results. Using the measured-to-predicted load distributions and the updated (or posterior) measured-to-predicted bearing capacity distributions, resistance factors were calibrated (or updated) from the first-order reliability method (FORM) for two different target reliability indices, 2.33 and 3.0. This research attempted to use the results of proof pile load tests, which are generally conducted to verify pile designs, to update resistance factors. The updated resistance factors varied substantially depending on the proof pile load test results. Therefore, the Bayesian implementation can contribute to economical pile designs. 相似文献
11.
通过高应变动测试验和静载荷试验,对深厚软土地基中PHC管桩的受力特性进行了研究,探讨了深厚软土地基中超长PHC管桩的竖向承载特性和荷载传递机理.结果表明,高应变动测试验和静载荷试验得出的极限承载力结果很接近.在深度小于30 m时,动静试验所得的侧摩阻力比较接近,但是随着深度的加深,动测试验所得的侧摩阻力比静载试验要大. 相似文献
12.
预制静压桩静动载现场试验分析 总被引：2，自引：0，他引：2
原位试验是获取桩基设计参数和了解桩基力学性能的最客观、最可靠方法。基于现有疲劳机和千斤顶等试验设备,研制了桩顶静载和动载组合加载装置,为现场静、动载试验解决了一个技术性难题。利用该装置对某工程混凝土预制静压桩进行了模拟交通荷载的现场静、动载试验。通过单桩竖向抗压静载试验和动载试验,分析了静动载对桩身轴力分布、桩身侧摩阻力和基桩沉降的影响及其变化规律。试验结果表明：在静动载作用下桩身侧摩阻力的分布规律基本一致,并且随着振动次数的增加,桩身上部侧摩阻力减小、下部略有增加,但动载循环超过30万次后,侧摩阻力趋于稳定。 相似文献
13.
Load displacement response and ultimate resistance of piles in sand under uplift load are predicted by load transfer approach.
The pile is divided into number of segments and assigned geometrical and material properties according to actual soil pile
situation. The shaft resistance is obtained analytically in accordance with existing studies. The proposed method takes into
account the length, diameter and relevant surface characteristics of pile and soil properties. The load displacement characteristics
and the value of uplift capacity of vertical piles from field test have been predicted. Reasonable agreement has been found
out between predicted and observed values of uplift capacity. Load transfer mechanism is capable of predicting the nonlinear
variation of load-displacement response of piles. 相似文献
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Coupled deformation–seepage analysis of dynamic capacity tests on open-ended piles in saturated sand
Open-ended piles such as tubular piles or I-beams are used as foundations for offshore and nearshore construction. After the pile installation a load test to estimate the bearing capacity of these open-ended piles is necessary. Due to the offshore conditions and the high bearing capacity of the installed piles a static load test is not normally feasible. Therefore, dynamic load tests are carried out where the wave propagation due to an dynamic impact at the pile head is measured. The methods to estimate the bearing capacity from the measured signal of the dynamic tests were derived for solid pile profiles. It is questionable whether these evaluation techniques are applicable for open-ended piles. Hence, the influence of various important system parameters as well as the differences between static and dynamic load tests on open-ended piles is investigated in this paper. 相似文献
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18.
超长PHC管桩桩顶沉降特性的动静对比分析 总被引：1，自引：1，他引：0
通过静载荷试验可直接测到桩顶的荷载-沉降（Q-s）曲线。由管桩内预先埋设的应变计的内力测试结果可计算出土阻力与桩-土相对位移的关系,并进一步做高应变测试和拟合分析,得出了高应变拟合的Q-s曲线。对Q-s曲线作动静结果对比分析,探讨了在深厚软土中的超长PHC管桩的桩顶沉降特性。结果表明,当荷载不大时,高应变拟合的沉降大于静载实测的沉降,但当荷载接近极限值时高应变的沉降小于静载的沉降。结果亦表明,当超长PHC管桩桩身穿过一定深度的好土层、桩端进入全风化或更好的岩层时,不管是静载试验还是高应变动力测试,都很难使土阻力得到充分发挥,此时静载实测的和高应变拟合的Q-s曲线都呈缓变型特征。 相似文献
19.
Behnam Ghorbani Ehsan Sadrossadat Jafar Bolouri Bazaz Parisa Rahimzadeh Oskooei 《Geotechnical and Geological Engineering》2018,36(4):2057-2076
This study explores the potential of adaptive neuro-fuzzy inference systems (ANFIS) for prediction of the ultimate axial load bearing capacity of piles (Pu) using cone penetration test (CPT) data. In this regard, a reliable previously published database composed of 108 datasets was selected to develop ANFIS models. The collected database contains information regarding pile geometry, material, installation, full-scale static pile load test and CPT results for each sample. Reviewing the literature, several common and uncommon variables have been considered for direct or indirect estimation of Pu based on static pile load test, cone penetration test data or other in situ or laboratory testing methods. In present study, the pile shaft and tip area, the average cone tip resistance along the embedded length of the pile, the average cone tip resistance over influence zone and the average sleeve friction along the embedded length of the pile which are obtained from CPT data are considered as independent input variables where the output variable is Pu for the ANFIS model development. Besides, a notable criticism about ANFIS as a prediction tool is that it does not provide practical prediction equations. To tackle this issue, the obtained optimal ANFIS model is represented as a tractable equation which can be used via spread sheet software or hand calculations to provide precise predictions of Pu with the calculated correlation coefficient of 0.96 between predicted and experimental values for all of the data in this study. Considering several criteria, it is represented that the proposed model is able to estimate the output with a high degree of accuracy as compared to those results obtained by some direct CPT-based methods in the literature. Furthermore, in order to assess the capability of the proposed model from geotechnical engineering viewpoints, sensitivity and parametric analyses are done. 相似文献