The paper presents numerical and experimental research on glulam delamination in a double lap connection with predominant shear stresses. Laboratory tests and wide literature survey enabled to determine timber and glue joint parameters. Cohesive zone theory, generally used for epoxy matrix and fiber reinforced composites, was adopted to modelling glue layer delamination in glulam elements. Numerical models were validated with laboratory tests.
The paper presents research program of bond between glass fiber reinforced polymer bars and concrete in reference to the steel bars. Bond between the reinforcement and concrete is a crucial parameter governing a behaviour of reinforced concrete members and transferring of the internal forces from concrete to the reinforcement. The use of FRP bars as an equivalent reinforcement to steel in concrete structures has increased in recent years. The FRP bars are very different from steel, mainly due to much lower elasticity modulus and their anisotropic structure. Good performance of FRP reinforced concrete requires sufficient interfacial bond between bars and concrete. However, there are no specific standards referring to the surface preparation of these bars, that leads to variable bond behaviour of the composite reinforcement to the concrete. The objective of the study was to investigate the influence of variable parameters on the bond behaviour to concrete. The experimental program consisted of eighteen beam bond specimens varying in: bar diameter (12 mm, 16 mm, 18 mm) and type of reinforcement (GFRP sand – coated and steel bars). Although the GFRP bars indicated good bond behaviour to concrete, the average bond strength was slightly lower than that of steel reinforcement of 16mm and 18 mm, while it was higher for the GFRP bars of 12 mm diameter.
The unmanned underwater tracked bulldozer (UUTB) is an indispensable equipment for dredging and cleaning obstacles on the river bed in the flood season. The investigation on the interaction properties between the UUTB tracks and sediments provides foundation for the evaluation of operation performance when it works on the inland river bed. Based on the current worldwide research, the sediments mixed by sand, bentonite and water with sand content 0%, 10% and 20% were configured in this study to replace the real sediments on the inland river bed in China. The current pressure-sinkage model and shear stress-shear displacement model were discussed. Three different tracks were tested for the pressure-sinkage and the shear stress-shear displacement on the platform. The relationship between pressure and sinkage under sand content 0%, 10% and 20% are revealed based on the experimental results. The modulus of cohesive deformation and friction deformation of the sediments under said sand content are presented. The curves of shear stress and shear displacement are also obtained, which demonstrates the properties between the tracks and configured sediments under sand content 0%, 10% and 20%. The relationship between the tractive force and slip ratio with three different tracks under said sand content is also presented based on the quantitative analysis, which provides reference for the dynamics control and performance evaluation of UUTB on the inland river bed.
The article concerns modern, flexible adhesive joints, which might be used in timber construction. The article discusses the test results carried out for timber elements joints using polymeric adhesives produced by Sika®. The scope of the tests includes the analysis of strength criteria, tests of polymer adhesion to the timber with a pull-off method, tests of polymer layer shearing between timber elements as well as examination of bending of timber elements joined with polymer. The conclusions indicate the types of these polymers which are recommended for the creation of polymeric joints of timber-polymeric type in timber constructions.
In the paper the results of experimental investigations concerning flat slabs made from reinforced lightweight concrete with sintered fly ash aggregate CERTYD were presented. In the research program 6 models made in a natural scale were included. The main variable parameter was slab longitudinal reinforcement ratio. The aim of investigation was the experimental verification of efficiency of double-headed studs as punching shear reinforcement. In the existing technical approvals such kind of reinforcement was allowed only in normal concrete slabs. It was demonstrated that double-headed studs can be an effective transverse reinforcement of lightweight aggregate concrete slabs. The use of double-headed studs resulted in increase in the ultimate load from 19% to 44%, depending on the slab reinforcement ratio which ranged from 0.5% to 1.2%. The comparative analysis showed that the Eurocode 2 provisions were conservative in relation to the experimental results, which were on average 42% higher than the theoretical ones however with a very low 7% coefficient of variation.