Applied Mechanics and Materials Vols. 284-287

Abstract: This paper examines an analysis model for predicting the tip capacity of drilled shaft foundations under gravelly soils. Forty one static compression load test data are utilized for this purpose. Comparison of predicted and measured results demonstrates that the prediction model greatly overestimates the tip capacity of drilled shafts. Further assessment on the model reveals a greater variation in three coefficients; the effective overburden pressure ( ), the overburden bearing capacity factor (Nq); and the bearing capacity modifier for soil rigidity (ζqr). These factors are modified from the back-analysis of the drilled shaft load test results. Varying effective shaft depths are considered for the back-calculation to explore their effects on capacity behavior. Based on the analyses, the recommended effective shaft depth for the evaluation of effective overburden pressure is limited to 15B (B=shaft diameter). The Nq and ζqr are enhanced while maintaining their basic relationship with the soil effective friction angle, in which the Nq increases and ζqr decreases as increases. Specific design recommendations for the tip bearing capacity analysis of drilled shafts in gravelly soils are given for engineering practice.

Abstract: The reinforced concrete (RC) buildings commonly used in Taiwan not only create great pollutions in material manufacturing and construction phases but also destroy the environment. On the other hand, the light weight steel buildings are safe, healthy, comfortable, producing less waste, and environmental friendly. Therefore, light weight steel buildings have been promoted in Taiwan by the government as an important “green building” policy. In Taiwan, there is still a large market of low rise light weight steel housing. To promote light weight steel housing in Taiwan, we should evaluate its influence on environment. In this research, we established a CO2 emission database for light weight steel building materials and calculated CO2 emission for a light weight steel house. The results showed that a low rise light weight steel house has 39% less CO2 emission than an RC house in the same scale. A light weight steel house has a good building envelope that decreases energy consumption of air-condition by 35.42-42.95%. Therefore, a light weight steel house has less CO2 emission from building materials and energy consumption than an RC house.

Abstract: A series of retrofitted extended end-plate connections have been tested experimentally and evaluated using the component method specified in Eurocode 3. The component method decomposed the end-plate connection into several components, including the tension zone, compression zone, vertical and horizontal shear zone that occurred at the bolt, end-plate, beam and column. Based on the theoretical model, the moment resistance and the initial stiffness of a connection can be predicted. Four experimental tests on the retrofitted extended end-plate connections have been conducted to verify the proposed design method. From the experiment tests, all moment resistance of the connections showed good agreement with theoretical predictions, which establish a reliable foundation to predict the moment resistance of the retrofitted end-plate connection. All initial stiffnesses calculated from theoretical predictions do not represent the actual behaviour of tested connection. All tested connections can be classified as partial strength based on EC 3: Part 1.8, in condition the welding capacity is at least 50% higher than the capacity calculated from the component method.

Abstract: The evaluation for double-angle compression members is a tedious procedure and is not an easy task for practicing engineers. In this study, a computer program has been developed to calculate the Pu based on the AISC specifications. It is found that the calculated value is quite close to the tabulated one if effective length (KL) is longer than 10 feet. However, the Pu is not tabulated for effective length less than 10 feet in some lager sections. It is found that the differences between the calculated value and the interpolated value could be as much as 20%. Unfortunately, the difference errors are not on conservative side and the use of interpolated values is not acceptable in practice. This study evaluates all double-angle compressive formulas provided by the AISC manuals and the comparisons among them are presented. The Pu versus KL curves, in which effective lengths less than 10 feet are added and plotted. Some supplementary tabulated values, which required in routine design and not listed in current AISC design manuals, are also furnished. This study will fulfill the needs for those who seek higher performance and wider coverage when evaluating the design of double-angle compression members under flexural-torsion condition.

Abstract: Johore, the southern part of west peninsular Malaysia is found to be rich in peat soil, especially at the Pontian & Batu Pahat district. The physico-chemical properties of the peat soil at the region had been extensively studied by various researches but limited studies were based on the interface layer of peat soil and non organic soil. The behaviour of the interface layer soil is believed to be governed by its organic matter content. Three locations of Batu Pahat, namely Parit Nipah, Parit Sidek & Batu Puteh which are difference in terms of geography setting were chosen in this case study. The main objective of this study is to characterize the geochemistry properties of the organic soil as a guide of its engineering behaviour. The soil specimens were collected using peat auger and undisturbed sampler. The organic contents and types of organic were determined in laboratory based on Loss on Ignition at 440c, carbon content and its molecular functional group. The pH, sulphate content, chloride content and cation exchange capacity (CEC) of the organic soil were also determined as a guide of its potential stabilization by using chemical stabilizer. X-ray fluorescence (XRF) and Fourier Transform Infrared (FTIR) were utilized to determine the bulk chemical composition of the soil and its functional group, respectively. The findings of this study are expected to give a better overview of organic soil which enable designer to have a better understanding when dealing with this kind of material.

Abstract: The Chi-Chi earthquake caused significant loss of property and life. This phenomenon disclosed many design-related in the construction industry. The first condition that we would like to determine is whether the earthquake affected the final strength of newly-cast concrete if the fresh concrete was cast just before the earthquake struck, particularly when the fresh concrete was cast just before its initial or final setting. This study aims to investigate the effects of an earthquake on fresh concrete. Twenty specimens were fabricated to investigate the effects of strong ground motion on concrete. Of the 20 specimens, 9 were lightweight-concrete-filled CFT (Concrete Filled Tube) columns, 9 were CFT columns filled with concrete of normal weight, and the remaining two were pure steel hollow tubes. The specimens were leveled on a shaking table to simulate the strong ground motion caused by an earthquake. The test reveals that the lightweight-concrete-filled CFT columns are unaffected by the quake. However, the normal weight concrete filled CFT columns are slightly affected by the quake.

Abstract: Bridges are prone to suffer from multiple hazards such as earthquake, wind, or floods for the special structural characteristic. To guarantee the stability of bridge structure, how to precisely evaluate the scour depth of bridge foundation has become an important issue recently as most of the unexpected damage or collapse of bridges are caused by hydraulic issue. In this paper, a vibration-based bridge health monitoring system considering the response of superstructure only is proposed to rapidly evaluate the embedded depth of bridge column. To clarify the complex fluid-solid coupling phenomenon, the effect of embedded depth and water level was first verified through a series of static experiment. A finite element model with confinement simulated by soil spring was then established to illustrate the relationship between the fundamental frequency and the embedded depth. With the proposed algorithm, the health condition of the bridge can be inferred by processing the ambient vibration response of the superstructure. To implement the proposed algorithm, a SHM prototype system monitoring the environmental factors such as temperature, water level, and inclination was developed to support on-line processing. The performance of the proposed system was verified by a series of dynamic bridge scour experiment conducted in laboratory flume and compared with the reading from water-proof camera. The result has shown that by using the proposed vibration-based bridge health monitoring system, the embedded depth of bridge column during complex scour process can be reliably reflected.

Abstract: Hazard control of explosion-induced vibration is an important issue which cannot be ignored in blasting engineering. Its influence range and damage scale are affected by the shock wave energy. This study applied the LS-DYNA software and adopted the Arbitrary Lagrangian-Eulerian method for numerical analysis to simulate the propagation of blast waves caused by the surface blast of C-4 explosives in a semi-infinite space in order to explore the effectiveness of Open Channel Grooves in vibration isolation. The analysis shows that the finite element method can properly simulate the dynamic characteristics of soil in an explosion; with the distance moving away from the explosion point, the shock wave gradually decays. Open Channel Grooves have a significant effect on attenuating the propagation of detonation waves. The attenuation degree is related to the width and depth of the groove, and the impact of the depth is greater than that of the width. This study can be used as a reference in hazard control of explosion-induced vibration for relevant engineering projects.

Abstract: This study used synchronized acoustic and optical nondestructive AE and ESPI technology with an inclined shear test to investigate the micro- and macroscopic failure mechanisms of cement mortar specimens under shear force. Crack opening displacement feedback was used to control stable damage to obtain complete loading curves of specimens sheared at different shear angles (β). AE technology was used to investigate the time and space distributions of the occurrence of microseismic sources produced by shearing within rocks. Synchronized comparisons were made using the interference images caused by the exterior of the rock material changing shape because of the shearing detected by electronic speckle pattern interferometry (ESPI). This was then used to examine three characteristics of the fracture evolution of rock-like material: localization, initiation of cracks, and crack propagation. The results indicate that shearing stiffness and shear strength are reduced following increases in the shear angle. In addition, the fracture propagation angle tends to change direction and its value also increases. Using AE methods to observe the evolution of microcracks in materials, the time and position of their localization were determined. These results were then compared with the crack initiation and propagation positions detected using ESPI. It is found that the fracture trends observed using these two methods were largely identical.

Abstract: The relationships among soil, sand, cement binder and compaction pressure were considered in this paper. The soil grading was investigated with particle sizes which are, in particular order, finer than 5, 1.18, 0.6, 0.3 and 0.15 mm. Corresponding to each of soil grades, the compaction pressure was applied in the range from low to high level. The influence of soil grading and compaction pressure could be determined by value of compressive strength, dry density and water absorption. The experimental results reported in term of the optimal proportion for mixture, which gave the best strength in each level of compaction pressure and size of soil particles. In addition, the conclusion about the influence of clay content on characteristics of compressed cement-soil materials was also figured out so that the suitable clay content in the optimal mix proportion for practical application could be determined.