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To study the durability of concrete with fly ash as fine aggregate subjected to alternative attacks of freeze-thaw and carbonation, the appearance, mass loss, relative dynamic modulus of elasticity, relative compressive strength, and carbonation depth of the concrete are investigated using cyclic tests under single carbonation, single freeze-thaw, and alternation of freeze-thaw and carbonation. In addition, microstructural analysis techniques including scanning electron microscope and X-ray diffraction are adopted to reveal the deterioration mechanism of alternating freeze-thaw and carbonation. Results show that carbonation is beneficial for refining the pore structure and increasing concrete strength in the initial alternative cycle, which delays the damage from freeze-thaw cycles. Damage from freeze-thaw causes crack propagation in concrete, which leads to carbonation intensification. Compared with other test modes, concrete under alternative freeze-thaw and carbonation causes the greatest degree of deterioration during the initial freeze-thaw cycles. The carbonation depth under alternative freeze-thaw and carbonation is positively correlated with the carbonation time and the water-to-cement ratio. However, as the reactant is continuously consumed due to the expansion of crystalline ice and CaCO3, alternative cycles result in the appearance of many more new cracks in the concrete.

Although various studies related to the punching shear strength of slabs have been published, databases related to punching shear strength are small in size. A database of 313 specimens has been structured through the present study, compared to the 114-data compiled by Kakuta et al. (1974) and the 138 data compiled by Gardner et al. (1996). In this study, six equations for the punching shear strength prescribed in specifications were evaluated based on the database. This paper includes a discussion of the parameters of punching shear strength in JSCE and AIJ specifications. A simplified strength equation is also proposed from the database.

Uneven foundation settlement is one of the common engineering problems in a collapsible loess area. In order to study the influence of uneven foundation settlement on the seismic performance of a structure, the incremental dynamic analysis (IDA) method is used to analyze the seismic vulnerability of the steel structure frame. The differences in the seismic response of the structure in relation to uneven foundation settlement are analyzed. The influences of uneven foundation settlement quantities and various areas of uneven settlement on the seismic response of the structure are discussed. On this basis, the relationship between ground motion intensity and structural failure probability is studied, by changing the magnitude of seismic acceleration peaks. Compared with the unsettled structure, the internal force redistribution of the structure caused by uneven foundation settlement is one of the causes of earthquake damage for some components. The uneven foundation settlement located at the corner of the plane of the structure is likely to cause more serious earthquake damage to the structure. Uneven settlement will cause an increase in storey drift. With the increase in settlement, the seismic damage of the superstructure will be aggravated.