Full-Scale Field Test On Retaining Structure Enhanced With Soil Nails And Prestressed Anchors

Retaining structure enhanced with soil nails and prestressed anchors is found good at constraining the horizontal displacement and therefore ensuring the stability of the foundation pit during excavation. Based on these advantages, such retaining structure is widely used in foundation excavation practice. This paper presents results of a series of in-situ tests conducted to investigate the mechanical behaviors of retaining structure enhanced with soil nails and prestressed anchors. Behaviors of three different retaining structures enhanced with i) soil-nails; ii) soil-nails and prestressed anchors without unbonded part; iii) soil-nails and prestressed anchors with a 2.5m unbonded length, were monitored during staged excavation to investigate the influences of i) the prestressing force and ii) unbonded length of the prestressed anchors on the performance of the entire retaining system. It was found that the affecting the stress and deformation of composite retaining system, which is in agreement with the other published results in the literature. The variation of the magnitude and distribution of soil nail force responding to the anchor prestressing force however showed no systematic trend. The unbonded length of anchors, which is suggested to be the main factor affecting the structural stability in dense materials in the literature, is found to have little influence in loose fill materials used in this study. Studies presented in this paper are useful for the rational design and serviceability analysis of the composite soil-nailed retaining structure enhanced with prestressed anchors.

Seismic Performance of Precast Columns Connected with Two Different Connection Modes

The precast reinforced concrete building is made of precast components, which are connected at the joints via reliable connection approaches. Therefore, the study on the stability and reliability of the connections should be conducted to improve the safety and integrity of the precast structure. In this paper, experiments on two connection modes, i.e. corrugated pipe confined with spiral stirrup connection and steel sleeve connection, were carried out. The experimental tests consisted of six specimens, including one cast-in-situ specimen, three precast specimens using steel sleeve connection and two precast specimens using corrugated pipe confined with the spiral stirrup. The influence of artificially unbonded length at the connection joint is also studied. All specimens were tested under low-frequency cyclic repeated loading to analyse their seismic performance under different connection modes. The experimental results showed that the precast columns using the two proposed connections have a similar or even better seismic performance compared with the cast-in-situ column. The installation of proper unbonded treatment on the longitudinal reinforcement in the connection is beneficial in improving the seismic performance of precast columns and the length of 5 times of the longitudinal reinforcement’s diameter is recommended.

Load transfer on instrumented prestressed ground anchors in sandy soil

abstract: This study evaluates load variations in instrumented prestressed ground anchors installed in a bored pile retaining wall system in sandy soil. Data were collected from instrumentation assembled in the bonded length of three anchors, which were monitored during pullout tests and during different construction phases of the retaining wall system. Instrumentation consisted of electrical resistance strain gauges positioned in five different sections along the bonded length. Skin friction distributions were obtained from the field load measurements. Results showed that the skin friction followed a non-uniform distribution along the anchor bonded length. The mobilized skin friction concentrated more intensely on the bonded length half closest to the unbonded length, while the other half of the bonded length developed very small skin friction. The contribution of the unbonded length skin friction to the overall anchor capacity was significant and this should be accounted for in the interpretation of routine anchor testing results. Displacements applied to the anchor head were sufficient to mobilize the ultimate skin friction on the unbonded length, but not on the bonded length. Performance of loading-unloading stages on the ground anchor intensified the transfer of load from the unbonded length to the bonded length. Long-term monitoring of the anchor after lock-off revealed that the load at the anchor bonded length followed a tendency to reduce with time and was not significantly influenced by the retaining wall construction phases.

Buckling of an Elastic Plate/Layer Along a Rigid Base With Adhesion

An infinitely long elastic plate/layer is under uniaxial compression with its long dimension held by adhesion to a flat rigid base without friction. A prescribed length of the plate/layer is free of adhesion. This configuration is similar to a pre-stressed elastic film for which buckling of an unbonded section is a necessary, but not sufficient, condition for delamination. For that configuration, buckling occurs at the Euler buckling load of a fixed–fixed plate. Although the present study does not include friction or tangential interface stresses, the onset of buckling should be similar for these two cases. For the case of an elastic plate, a cohesive zone is used and it is found that the fixed–fixed buckling load is not attained except for extremely large values of a cohesive zone parameter. For realistic values, the buckling load is about half of that value. For the situation of an elastic layer with adhesion (without a cohesive zone), the buckling load approaches the fixed–fixed value only for very large values of the ratio of the unbonded length to the thickness.

Analysis on Factors Affecting the Self-Repair Capability of SMA Wire Concrete Beam

Crack expansion of concrete is the initial damage stage of structures, which may cause greater damage to structures subject to long-term loads or under extreme conditions. In recent years, the application of intelligent materials to crack self-repair has become a hotspot among researchers. In order to study the influence of factors on the self-repair capability of shape memory alloy (SMA) wire concrete beam, both theoretical and experimental methods were employed for analysis. For the convenience of experiment, composite materials (epoxy cement mortar and silicone polymer clay) instead of concrete were used. The SMA wires were externally installed on and internally embedded in epoxy resin cement mortar beams and silicone polymer clay beams. Comparison of crack repair situation between two installation methods turns out that both methods possess their own advantages and disadvantages and should be employed according to the actual situation. The influence of unbonded length on the self-repair capability of embedded type SMA wire beams and the necessary minimum unbonded length to achieve self-repair function were studied. The results state clearly that the longer the unbonded length is, the better the crack repair situation is.

Deflection and Crack-Width Prediction of Partially Boned CFRP Concrete Beams

Concrete beams reinforced with fiber reinforced polymer(FRP)bars exhibit large deflections and crack widths as compared to concrete beams reinforced with steel due to the low modulus of elasticity of FRP. Consequently,in many cases,serviceability requirements may govern the design of such members. This paper describes six partial bonded concrete beams prestressed with CFRP tendons are tested under monotonic loads. deformation and crack width of this kind of beams with varying unbonded length are systematically investigated. The predictions of the 《Code for Design of Concrete Structures》（GB50010－2002）equations are compared with the experimental results obtained by testing six partial bonded concrete beams prestressed with CFRP tendons. Good agreement was shown between the theoretical and the experimental results.

MODELLING of Delfcetion Performance in Partially Bonded CFRP Prestressed Beams

six partial bonded concrete beams prestressed with CFRP tendons are tested under monotonic loads. deformation of this kind of beams with varying unbonded length are systematically investigated. full-range analysis for deflection performance of partial bonded CFRP prestressed beams is performed by using ADINA. The analytical results agree well with the experimental results.