Long-term Loading Tests Research Articles

Long-term performance of reinforced concrete beams with carbon-fiber sheet

For applications in the civil and building engineering area of the retrofitting method using carbon-fiber sheet, the behavior of durability and long-term performance of reinforced concrete members under live loads should be grasped. This paper describes about the long-term performance of reinforced concrete beams with carbon-fiber sheet. As a result of long-term loading tests for the last 4 years, it was concluded that the retrofitting system using carbon-fiber sheets is successful to increase the flexural strength and to prevent the increase of long-term deflection on the existing reinforced concrete beams or slabs, in the manner as seismic reform of columns in buildings and the pier of bridges.

Comparison of concrete slabs pretensioned with composite bars and steel wires

A test program was set up to study AFRP as prestressing reinforcement for concrete slabs. The paper describes short-term, long-term and cyclic loading tests on ten slabs. The structural behavior of the pretensioned slabs, under these loading conditions, is investigated. Finally, it is concluded that the use of AFRP as prestressing reinforcement can offer promising perspectives.

Long-Term Performance of Prestressed, Pretensioned High Strength Concrete Bridge Girders

An experimental investigation of high strength concrete bridge girders was conducted. The investigation included fabrication and testing of 70 ft long, 54 in. deep pretensioned, prestressed high strength concrete bulb-tee girders. The design concrete compressive strength for the girders was 10,000 psi. Two girders were used to evaluate long-term static load and fatigue performance. Results from girder used to determine long-term static load behavior indicated prestress losses that were significantly less than those predicted by the AASHTO Standard. The girder used to determine fatigue performance withstood more than 5 million cycles of fatigue loading and satisfied all serviceability requirements. Upon completion of the long-term static load and fatigue test, measured flexural properties for both girders were adequate with respect to both design and specification requirements. Based on results from this investigation, high strength concrete bridge girders can be expected to perform adequately over the long-term when designed and fabricated in accordance with current AASHTO provisions.

Construction control for underpinning piles and their behaviour during excavation : Y. Iwasaki, H. Watanabe, M. Fukuda, A. Hirata & Y. Hori, Geotechnique, 44(4), 1994, pp 681–689

This paper describes a case history of cast-in-place concrete piling to support large underground structures for a subway in Nagoya city, Japan. The ground was medium-to-dense sand interbedded with clayey soil. Owing to geotechnical and construction conditions at the site, the piles had to be designed as friction piles. Based on full-scale short- and long-term load tests, ultimate bearing capacity and creep load characteristics were obtained. However, due to the uncertainty of friction on these bored piles, the performance of every pile was verified by load testing. One pile was found to be unsatisfactory and was treated to improve behaviour. Monitoring piles were installed with strain gauges to observe performance. When excavation started the axial load in the upper part of the pile increased while that in the lower part decreased. The reason for this was, at first, obscure. What had been expected was an increase in axial load from the top to the bottom. The site study - using measurements of pile-ground interaction - revealed that the effect was caused by ground heave resulting from the excavation. The observational procedure was useful, not only to confirm predetermined targets, but also to shed light on unexpected geotechnical problems. (A)

Construction control for underpinning piles and their behaviour

This Paper describes a case history of cast-in-place concrete piling to support large underground structures for a subway in Nagoya city, Japan. The ground was medium-to-dense sand interbedded with clayey soil. Owing to geotechnical and construction conditions at the site, the piles had to be designed as friction piles. Based on full-scale short-and long-term load tests, ultimate bearing capacity and creep load characteristics were obtained. However, due to the uncertainty of friction on these bored piles, the performance of every pile was verified by load testing. One pile was found to be unsatisfactory and was treated to improve behaviour. Monitoring piles were installed with strain gauges to observe performance. When excavation started the axial load in the upper part of the pile increased while that in the lower part decreased. The reason for this was, at first, obscure. What had been expected was an increase in axial load from the top to the bottom. The site study-using measurements of pile-ground interaction-revealed that the effect was caused by ground heave resulting from the excavation. The observational procedure was useful, not only to confirm predetermined targets, but also to shed light on unexpected geotechnical problems. L'article décrit un cas de pieux coulés sur place permettant de soutenir les grandes structures souterraines d'une autoroute de Nagoya, Japon. Le sol est constitué de sable moyennement à fortement dense intercalé de lits argileux. A cause des conditions géotechniques de construction sur le site, les pieux conçus sont des pieux frottants. La capacité portante ultime et les caractéristiques de fluage ont été mesurées lors d'essais de chargement pleine échelle à court et long terme. Cependant, en raison de l'incertitude pouvant exister sur le frottement le long de pieux forés, la performance de chaque pieu a été vérifiée lors d'essais de chargement. Un des pieux s'étant révélé peu satisfaisant, il a été traité pour améliorer son comportement. D'autres pieux ont été équipés de jauges de contrainte et suivis par enregistrement pour étudier leurs performances. Lorsque l'excavation commence, la charge axiale de la partie supérieure du pieu augmente tandis que celle de la partie inférieure décroît. Cette réponse est tout d'abord apparue bien étrange: on attendait une augmentation de la charge axiale sur tout le pieu. Une étude du site réalisée par mesure de l'interaction sol-pieu a cependant montré que cet effet était causé par une soulèvement du sol lors de l'excavation. La méthode d'observation a donc été utile, non seulement pour valider les objectifs fixés initialement, mais aussi pour éclaircir les problèmes géotechniques inattendus.

Long-Term Settlement Characteristics of a Friction Pile

ABSTRACT Long-term loading tests were performed on newly developed short friction piles during the period of four months. Eight test piles of 4.5 m long and 250-430 mm in diameter were installed by grouting mortar under the pressure of 0.7-1.0 MPa in bags woven by a synthetic fiber that had previously been inserted in drilled holes in a soft clayey soil. The long-term vertical loads were applied on the pile heads ranging from 21% to 44% of the pull-out capacity of the piles. Drained soil modulus and creep coefficient that describe the long-term settlement behavior of piles were derived from the observed pile head settlement vs. log time relationship. Both parameters are influenced by the ratio of the long-term applied load to the pull-out capacity,P/Pu.Drained soil modulus reduces with an increase ofP/Pu,demonstrating the soil non-linear characteristic, while creep coefficient remains in a fairly constant value. The ratio of the creep coefficient to the soil flexibility (inverse of soil modulus) lies in the range of 0.1-1.5 underP/Pu less than 0.4.

Time-dependent behaviour of simply-supported steel-concrete composite beams

A theoretical and experimental study of the time-dependent behaviour of composite steel-concrete structural members has been undertaken at the University of New South Wales. As part of the experimental investigation, long-term static load tests were carried out on four simply-supported composite steel-concrete beams. The deformations were monitored for a period of about 250 days, as were the creep and shrinkage characteristics of concrete specimens under the same ambient conditions as the test beams. Pushout tests were also conducted on the headed studs used as shear connectors in the test specimens, and slip deformations and slip strains were recorded for two different connector densities. In this Paper transverse deflexions are shown to agree well with a design proposal presented elsewhere. The experimental results presented here provide benchmark data for the calibration of more complex theoretical treatments that incorporate creep, shrinkage and connector slip.

関東ロームの長期沈下特性に関する研究 : 長期平板載荷試験結果について

This study is concerned with relationship between pressure and settlement observed from long-term elate loading tests on Kanto Loam. Conclusions are as follows ; (1) Settlement of Kanto Loam consists mainly of an initial, transient and Creep settlement. (2) Both of transient and creep settlement, after initial settlement, can be put on linear line when these settlements plotted on semi-logarithmic graph by taking time factor logarithm. (3) Rate of settlement in condition of transition and creep depend on unit weight, elastic modulus of Kanto Loam, plate width and depth of plate. (4) Predicting rate of creep settlement after 10 years is nearly equal to 10〜80 per cent of the initial settlement in long-term plate loading tests.

Long-term deflections of reinforced concrete beams

Synopsis Long-term static load tests were carried out on simply supported and continuous reinforced concrete beams at the N.S.W. Institute of Technology, Sydney, Australia. The instantaneous and time-dependent beam deflections were recorded, together with the time-varying strain distributions at selected cross-sections and the redistribution of bending moments due to creep and shrinkage. In this paper, the measured beam deflections are compared with values predicted by British and American design code methods and by finite element methods. The creep and shrinkage properties used in the predictions were obtained from test specimens and were also calculated in accordance with CP 110:1972, AS 1481–1978, ACI 209:1971 and the CEB–FIP 1978 Model Code. For the samples of concretes examined, the applicability of these predictive methods is discussed.

Long term anchor holding capacity in satured clays

The results of a laboratory model study investigating the behavior of deeply embedded anchors are presented. The primary purpose of the tests is to study the behavior of the anchor-soil system under long-term loading in saturated, normally consolidated clay.The tests were conducted in soil of two different shearing strengths. For each soil strength, three different long-term load tests were performed. Long-term loads applied were at stress levels equivalent to 25%, 50% and 75% of the short-term (undrained) anchor break-out capacity. Pore pressure responses around the anchor, including the negative pore pressure (suction) beneath the anchor, were monitored using miniature piezometric probes. The test results provided functional relationship between anchor displacement, anchor load and pore pressure responses associated with consolidation process.

Analysis of Creep Settlement of Pile Foundations

The problem of the settlement of a pile in a soil exhibiting creep properties is analyzed by converting the viscoelastic problem to an equivalent elastic problem by means of a Laplace transform. The solution in then found in Laplace transform space in the form of an eigenvalue expansion and transformed back to obtain a numerical solution to the original problem. Some typical solutions are presented for the settlement and base load transfer in a pile for two types of creep response, a terminating creep represented by a linear viscoelastic model and a nonterminating creep in which creep strain is a linear function of log time. This fact leads to a simple expression for the logarithmic creep settlement rate of the pile. The determination of the required soil parameters from long-term pile loading tests is considered and values backfigured from such a test are presented.