Vibration Serviceability of Large-Span Steel–Concrete Composite Beam with Precast Hollow Core Slabs Under Walking Impact

A large-span steel–concrete composite beam with precast hollow core slabs(CBHCSs)is a relatively new floor structure that can be applied to various long-span structures.However,human-induced vibrations may present serviceability issues in such structures.To alleviate vibrations,both the walking forces excited by humans and the associated floor responses must be elucidated.In this study,150 load–time histories of walking,excited by 25 test participants,are obtained using a force measuring plate.The dynamic loading factors and phase angles in the Fourier series functions for one-step walking are determined.Subsequently,walking tests are performed on seven CBHCS specimens to capture the essential dynamic properties of mode shapes,natural frequencies,damping ratios,and acceleration time histories.The CBHCS floor system generally exhibits a high frequency(>10 Hz)and low damping(damping ratio<2%).Sensitivity studies using the finite element method are conducted to investigate the vibration performance of the CBHCS floor system,where the floor thickness,steel beam type,contact time,and human weight are considered.Finally,analytical expressions derived for the fundamental frequency and peak acceleration agree well with the experimental results and are hence proposed for practical use.

Deflection and stress of hollow CRCP slab under concentrated vehicle load

Based on the equivalence principle of deflection and stress, the concentrated vehicle load which acts on the center of continuously reinforced concrete pavement （CRCP） is translated into the equivalent half-wave sine load by the Fourier transform. On the basis of this transform and the small deflection theory of elastic thin plates, the deflection and stress formulae of CRCP under the concentrated vehicle load with a hollow foundation are put forward. The sensitivity of parameters is analyzed. The results show that maximum deflection is directly proportional to the concentrated vehicle load and the slab width, and inversely proportional to the lateral bending stiffness and slab thickness. The effects of slab width and thickness are significant with regard to maximum deflection. Maximum stress is directly proportional to the concentrated vehicle load and the slab width as well as inversely proportional to slab thickness. The effect of slab thickness is significant with regard to maximum stress. According to the calculation results, the most effective measure to reduce maximum deflection and stress is to increase slab thickness.

Moment transfer factors for column-supported cast-in-situ hollow core slabs

Hollow core slabs are becoming of increasing interest as the construction industry attempts to minimise the impact of its activities on the environment. By forming voids in the interior of a concrete slab, the amount of concrete used can be reduced without significantly altering the capacity of the structure. In this study, we examined the inner force transfer mechanism of a column-supported cast-in-situ hollow core slab using finite element analysis. Both a hollow core slab and the corresponding solid slab were analysed using ANSYS and the results were compared. The orientation of the tube fillers causes the stiffness of the hollow slab to be orthotropic, potentially changing the distribution of load carried in the two orthogonal directions. Both the cross-section’s moments in the column strip and near the columns in the hollow core slab become larger than that in the solid floor. As well, the cross-section’s stiffness along the tube arrangement direction is larger than that of the radial cross-section, which causes the direction along the hole of the hollow core slab to carry more moment than the radial direction. The conversion factors of the two directions are proposed from the comparison for four typical areas of the hollow core slab, as are the moment distribution coefficients.

Distributed TLDs in RC floors and their vibration reduction efficiency

A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete （RC） floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluid- structure conpling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.