钻孔灌注桩单桩承载性状的试验研究

利用单桩竖向抗压载荷试验,对比分析未压浆和压浆的钻孔灌注桩单桩承载性能。结果表明:在极限荷载作用下,与未压浆钻孔灌注桩的桩顶位移相比,压浆后的钻孔灌注桩的桩顶位移降幅达到57.1%;卸载至0时,与未压浆钻孔灌注桩的桩顶位移相比,压浆后钻孔灌注桩的桩顶位移降幅达到67.9%;对于所有的钻孔灌注桩而言,其桩身轴力随着深度的增加而降低。当桩顶荷载较小时,桩身轴力-深度曲线相对较陡,随着桩顶荷载的增加,曲线开始渐渐变缓。桩顶荷载越大,桩端阻力占桩顶荷载的比例越高。极限荷载作用下,压浆后钻孔灌注桩的桩端阻力明显提升,增幅达到约50%;桩端阻力占比均小于25%。

Investigating the Effect of Fatigue on Fracturing Resistance of Rocks

There is no doubt that an understanding of brittle rock fracturing is a key element in the solution of many engineering problems that involve rock structures. Some rock structures such as bridge and dam abutments and foundations, and tunnel walls, undergo both static and cyclic loading caused by drilling and blasting, and vehicle-induced vibrations. This type of loading often causes rock to fail at a lower than its static strength due to the effect of rock fatigue. A series of laboratory diametrical compression tests was performed on Brisbane tuff disc specimens to investigate their mode-I fracture toughness response to static and cyclic loading, as a function of the applied load. Both the static and cyclic loading tests were carried out on CCNBD （cracked chevron notched Brazilian disc） rock specimens. In the tests described herein, the reduction in fracture toughness under dynamic cyclic loading was found to be up to 48% of the static fracture toughness. Contrary to the static tests, the cyclic tests produced much more crushed material in front of the tip of the chevron notched crack.

Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Compressive properties and energy absorption of BCC lattice structures with bio-inspired gradient design

Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)lattice to obtain specially designed mechanical behaviors,such as load-bearing and energy absorption capacities.First,a theoretical model is proposed to predict the initial stiffness of the gradient lattice structure under compressive loading,and validated against quasi-static compression tests and finite element models(FEMs).The deformation and failure mechanisms of the two structures are further studied based on experiments and simulations.The UGL structure exhibits a layer-by-layer failure mode,which avoids structure-wise shear failure in uniform structures.The BGL structure presents a symmetry deformation pattern,and the failure initiates at the weakest part.Finally,the energy absorption behaviors are also discussed.This study demonstrates the potential application of gradient lattice structures in load-transfer-path modification and energy absorption by topology design.