Responses of frozen fine-grained soils due to multiple packets of cyclic stress with variable-amplitude and an empirical prediction model

A suite of stress-controlled cyclic triaxial tests were performed on frozen fine-grained soils to assess the characteristics of the accumulated and cyclic behaviours under packets of cyclic stress with variable-amplitude. The influence of cyclic stress sequences is highlighted, and the results of the variable-amplitude cyclic tests indicate that the applied cyclic stress amplitude sequence is of significant importance regarding the final accumulated deformations. A step change is observed in the accumulated strain when the applied cyclic stress amplitude is beyond that of the previous stress package, while a decreasing level of cyclic stress below the previous loading package results in slight additional strain accumulation. The results of these tests also indicate that the cyclic stiffness is dependent on both the past accumulated strain and the current cyclic stress amplitude. For frozen soil, a higher past accumulated strain and lower cyclic stress levels yield a higher cyclic stiffness. An empirical approach for representing the response of frozen fine-grained soils under multiple packets of cyclic loading are proposed and then verified by the test data. The results show that the proposed empirical model is able to extract and predict the accumulated and cyclic behaviours under multiple packets of cyclic loading.

Tests on Steel and Composite Beam-to-Column Connections Strength and Stiffness Aspects

The connection interface of seven welded and bolted beam-to column connections under cyclic alternating loads, has been studied. Three fully welded connections were designed to compare the effect of filled-in concrete in a typical steel column section (a composite section) with the response of typical welded connections with and without column-web stiffeners. A similar set of three specimens were tested to assess the composite effect for connections with bolted endplates. A final, seventh, bolted beam-column connection, with composite sections for both the column and the beam, was also tested. The test results have demonstrated the effectiveness of concrete in replacing the stiffeners. Compared to the welded unstiffened connection, the use of bolted endplate connections or of composite column sections can increase the elastic moment-rotation stiffness of the connection, introducing however cyclic stiffness degrading phenomena when stressed beyond the elastic limit.