Preloading Stage Research Articles

A Model For Evaluating The Fire Resistance Of High Performance Concrete Columns

A numerical model, in the form of a computer program, for evaluating the fire resistance of high performance concrete (HPC) columns is presented. The three stages, associated with the thermal and structural analysis, for the calculation of fire resistance of columns is explained. A simplified approach is proposed to account for spalling under fire conditions. The use of the computer program for tracing the response of an HPC column from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in the program is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Details of fire resistance experiments carried out on HPC columns, together with results, are presented. The computer program can be used to evaluate the fire resistance of HPC columns for any value of the significant parameters, such as load, section dimensions, fiber reinforcement, column length, concrete strength, aggregate type, and fiber reinforcement without the necessity of testing.

A model for evaluating the fire resistance of contour-protected steel columns

A numerical model, in the form of a computer program, for evaluating the fire resistance of insulated wide-flange steel columns is presented. The three stages associated with the thermal and structural analysis in the calculation of fire resistance of columns is explained. The use of the computer program for tracing the response of an insulated steel column from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in the program is established by comparing the predictions from the computer program with results from full-scale fire tests. Details of fire tests carried out on wide-flange steel columns protected with ceramic fibre insulation, together with results, are presented. The computer program can be used to evaluate the fire resistance of protected wide-flange steel columns for any value of the significant parameters, such as load, section dimensions, column length, type of insulation, and thickness of insulation without the necessity of testing.

Experimental Evaluation of Consolidation Behavior of Stiff Clay Lumps in Reclamation Fill

Abstract When stiff clay dredged from the seabed is deposited by barge as fill material, large voids exist between the stiff clay lumps in the reclamation fill. One major concern is that the voids may close up upon loading, resulting in a large and sudden increase in the fill settlement. In the present study, an experimental investigation is carried out to examine the behavior of fill made up of dredged stiff clay lumps using a large one-dimensional compression apparatus and a centrifuge modeling technique. The results revealed that much of the inter-lump voids close up during the preloading stage. In addition, the rate of consolidation of the lumpy fill is significantly faster than that of homogeneous clay with the difference in consolidation rate diminishing with increase in loading pressure. The effects of lump shape and size, and original shear strength of in situ clay on the performance of lumpy fill, are also investigated.

An Experimental Study on the Effect of Curvature-Rate at Preloading Stage on Subsequent Creep or Relaxation of Thin-Walled Tubes under Pure Bending.

Pure bending with a constant curvature-rate followed by creep(hold constant moment for a period of time)or relaxation(hold constant curvature for a period of time)tests were conducted to investigate the effect of prior curvature-rate at preloading stage on the subsequent creep of relaxation behavior. Thin-walled tubes of 304 stainless steel were used in this investigation. The curvature-ovalization measurement apparatus, designed by Pan et al.(1) was used for conducting the present experiments. It has been found that the curvature-rate at the preloading stage has a strong influence on the subsequent creep or relaxation deformation under pure bending.

Effect of pre-loading damage on the net-lifetime of optimally prestressed rotating disks

The present paper is a direct extension of the paper [22], where various problems of optimal design of disks with respect to brittle rupture are formulated and discussed. In general, two ways to increase the disk lifetime have been proposed: thickness optimization in order to find disks of uniform creep strength, or optimization of the initial prestressing of disks of constant thickness in order to maximize the lifetime. A simultaneous control of both the disk thickness and the prestressing may result in a significant improvement of the disk lifetime. Initial prestressing is induced here by a peripheral elastic ring, which causes the creep damage growth during the stage of loading to be more uniform and gradual. The advantages of the improvement of the disk lifetime with respect to brittle rupture due to prestressing are found to be smaller when the pre-loading stage of creep of the disk, initiated by the prestressing ring action, is taken into account. Depending on the duration of the pre-loading stage of the creep process due to prestressing, a noticeable reduction of the net-lifetime during the stage of loading (due to rotation) may be observed.

Design and Performance of an Expressway Constructed Over Peat by Preloading

This paper presents the complete record of the laboratory investigations and field observations made in conjunction with the construction of expressway embankments built by preloading over a muskeg. The peat deposit, located on the north shore of the Saint-Laurent River, was initially 10–19 ft (3.0–5.8 m) thick and is underlain by sand. Settlements of the highway fills ranging from 5 to 11 ft (1.5 to 3.3 m) were measured during construction.Laboratory and field tests were performed before and during construction. Field vane tests made at the end of the preloading stage indicated a considerable gain in the shear strength as a result of consolidation. Compressibility characteristics of the peat measured in the laboratory are compared with the field behavior.Periodical field level observations were taken during the 4 years after the removal of the temporary surcharge and have shown that the highway embankments heaved 2–3 in. (5.0–7.5 cm) over a period of 12 months at a gradually decreasing rate. The rebound was followed by long-term secondary settlements totaling 0.5–1.5 in. (1.3–3.8 cm) over the following 3 years of observations. Analysis of the settlement records shows that preloading has been beneficial in reducing the coefficient of secondary compression of the peat. Preloading was simulated in the laboratory by means of oedometer tests on peat samples; both the laboratory results and the field observations revealed a remarkable agreement between the duration of the surcharge stage and the time for rebound to be complete after removal of the surcharge.