Safety analysis of pedestrian and roadway dimensional-dividing buildings

The safety performance of pedestrian and roadway dimensional-dividing buildings under seismic excitations are analysed. Considering the large displacement of the isolator bearing during earthquake, the gravity force becomes the dominant forces because of the accumulated permanent deformations in the building, which results in the structure collapse due to lateral instability. A mod- el is established based on an inelastic time history analysis to consider P - z~ effects in multi-degree- of-freedom. A safety criterion of the system is defined. The influence of the stiffness of an independ- ent column is revealed and compared with the influence of the shear force of the independent column to analyze the safety of the structures. Numerical results show that the special structure of pedestrian and roadway dimensional-dividing buildings can reduce the risk of the building in earthquake. The suitable section and height of the independent column greatly affect the building safety.

Strength Degradation of Wood Members Based on the Correlation of Natural and Accelerated Decay Experiments

An accelerated decay test and a natural decay test were conducted synchronically to explore the strength degradation of decaying wood members under long-term exposure to natural environment.A natural decay test was carried out to measure the bending strength,compressive strength parallel to grain and modulus of elasticity of the wood members,with 6 groups of specimens decayed in natural environment for 3 to 18 months respectively.To compare with corresponding decay test,in which 6 other groups of specimens were measured under accelerated conditions.The experimental data collected were evaluated by Pearson productmoment for the correlation.The results indicate that the mechanical properties of the accelerated decay were highly correlated with those in natural environment,both of which decreased in the same trend.Under the given test conditions,the mean value of the accelerated decay test data were curve-fitted to achieve the time-dependent degradation model of the bending strength,the compressive strength parallel to grain,as well as the modulus of elasticity.Due to the high correlation,the acceleration shift factors(ASF)of the two tests were derived,where the bending strength of 2.934,the compressive strength parallel to grain of 2.519 and the elastic modulus of 2.346 were employed to formulate the strength degradation models in the long-term natural environment.The results verify that the exponential function
σ=σ0e^(-βt)enables to exactly capture the degradation of the mechanical properties of wood members decayed in natural environment.

Unified strength model based on the Hoek-Brown failure criterion for fibre-reinforced polymer-confined pre-damaged concrete columns with circular and square cross sections

Fibre-reinforced polymer(FRP)has the advantages of high strength,light weight,corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns.Most of the existing strength models were built by regression analysis of experimental data;however,in this article,a new unified strength model is proposed using the Hoek-Brown failure criterion.To study the strength of FRP-confined damaged and undamaged concrete columns,900 test data were collected from the published literature and a large database that contains the cross-sectional shape of each specimen,the damage type,the damage level and the FRP-confined stiffness was established.A new strength model using the Hoek-Brown failure criterion was established and is suitable for both circular and square columns that are undamaged,load-damaged and fire-damaged.Based on the database,most of the existing strength models from the published literature and the model proposed in this paper were evaluated.The evaluation shows that the proposed model can predict the compressive strength for FRP-confined pre-damaged and undamaged concrete columns with good accuracy.

Experimental investigation on dynamic mechanical properties of sandy clay treated with alkali-activated metakaolin cement and discrete polypropylene fibers

The dynamic mechanical properties and dynamic energy absorption capacity of marine sandy clay,which was stabilized by cement with partial substitution of alkali-activated metakaolin(AAMK)and discrete polypropylene fibers,were experimentally investigated at strain rates of 80-280 s^(-1).The AAMK,as partial replacement of cement,is eco-friendly and economical,and polypropylene fibers with corrosion resistance can withstand severe environmental conditions.Dynamic mechanical properties of 16 different mix ratios were experimentally examined via split Hopkinson compression pressure bar(SHPB)tests.Typical macroscopic post-impact fragment patterns Ⅰ and Ⅱ were observed in dynamic stress-strain curves and macroscopic fragmentations.The results confirmed an obvious enhancement in the dynamic compressive strength and energy absorption density due to the use of cement with partial substitution of AAMK and the addition of polypropylene fibers and sand.Based on scanning electron microscopy(SEM)tests and nuclear magnetic resonance(NMR)tests,cemented sandy clay specimens treated with 0.2%fiber contents or higher exhibited a denser network of soil particles with hydration products.The connection mechanism and typical interface between fiber-sand-hydrate-sandy clay particles were observed via SEM tests.Furthermore,an optimal mix ratio was proposed to satisfy the demands of high dynamic mechanical properties,energy absorption capacity,and economic and environmental constraints.The optimal mix ratio corresponded to 0.2% fiber content or higher and sand content of up to 16%.Additionally,it was observed that the dynamic compressive strength of samples with 0.1% fibers or less deteriorated.Based on absorption energy density and failure modes analysis,the fiber content should be higher than or equal to 0.2% to effectively reduce the degree of fragmentation and increase the size of fragments.