Experimental Research On Novel Prefabricated Glubam-concrete Composite Beams

Currently,the experimental researches and applications of timber/bamboo-concrete composite（TCC/BCC）beams are mainly focused in"wet"connection,corresponding that upper concrete slab connects with timber/bamboo beam by the measure of cast-in-situ.This method exhibits obvious shortcomings such as low construction efficiency,poor mechanical properties and increasing the long-term deformation of TCC/BCC beams under the long-term load.Prefabricated composite beams based on the"dry"connection can effectively overcome the aforementioned problem,and it is of a new research field in the TCC/BCC.Designing novel connectors with rigid,strong,ductile,easy assembly,and easy construction is the key for developing the prefabricated TCC/BCC.Based on the combination of reactive powder concrete（RPC）and threaded rod,a new type of composite connector,named as Plug-in RPC-threaded rod composite connector（P-connector）,was proposed and carried out the put-out tests.Three large-scale BCC beams with typical P-connectors were also performed the bending tests in order to evaluate the construction method and evaluate the bending capacity of the BCC beams.The main results can be drawn,as follows:（1）Twelve groups of test samples were carried out the put-out tests,in which the concrete slab thickness and the anchorage length of the P-connector were selected as test parameters.The results indicate that the density of bamboo block embedded in the concrete slab has a significant effect on the shear stiffness of P-connector.Generally,the shear stiffness increases as increasing of the connection length.However,the increasing rate gradually declines with the enlarging connection length.Increasing the thickness of the embedded bamboo block in concrete slab can improve the shear performance of the P-connector,while this increasing trend is relatively stable by using too thick bamboo block.（2）Nine groups of test samples were carried out the pullout tests considering the outside diameter and the rod diameter as the parameters.,The results show that the bearing capacity and shear stiffness of P-connector increase with enlarging the outside diameter and the rod diameter.Relatively,the influence from the outside diameter on the performance of the P-connectors is greater than from the rod diameter.The ratio of RPC area and rod area(A_rpc/A_s)should not be more than 12 for acceptable ductility of P-connectors.（3）Three large-scale BCC beams with the typical P-connectors were carried out bending tests.The results show that the equivalent spacing of connectors has an important effect on the bending performance.Bending stiffness of BCC beams increases with the connector spacing decreases,while its ductility deceases synchronously.Increasing the thickness of concrete slab can improve the ductility of BCC beam.On the other hand,the self-weight of BCC increases with selecting the thicker slab,and it results in relatively limited enhancing effect by using thick concrete slab.（4）Finite element model of prefabricated BCC beams was established by Abaqus,and the validity of the model was also verified with the experimental data.Then,the model was used to calculate and analyze the bearing performance of BCC beams with different equivalent spacings of P-connectors.The results show that the equivalent spacing has reasonable upper and lower limits according to the ductility requirement.In order to ensure necessary ductility of the BCC beams before failure,the lower limit and upper limit for the typical P-connector can be taken as 225mm and 500mm,respectively.The novel composite connector and relatively design methods proposed in current study provide basic data for further investigations and application of this type of prefabricated BCC structure.