Seismic Performance of Precast Columns Connected with Two Different Connection Modes

The precast reinforced concrete building is made of precast components, which are connected at the joints via reliable connection approaches. Therefore, the study on the stability and reliability of the connections should be conducted to improve the safety and integrity of the precast structure. In this paper, experiments on two connection modes, i.e. corrugated pipe confined with spiral stirrup connection and steel sleeve connection, were carried out. The experimental tests consisted of six specimens, including one cast-in-situ specimen, three precast specimens using steel sleeve connection and two precast specimens using corrugated pipe confined with the spiral stirrup. The influence of artificially unbonded length at the connection joint is also studied. All specimens were tested under low-frequency cyclic repeated loading to analyse their seismic performance under different connection modes. The experimental results showed that the precast columns using the two proposed connections have a similar or even better seismic performance compared with the cast-in-situ column. The installation of proper unbonded treatment on the longitudinal reinforcement in the connection is beneficial in improving the seismic performance of precast columns and the length of 5 times of the longitudinal reinforcement’s diameter is recommended.

New Technique to Improve the Ductility of Steel Beam to Column Bolted Connections: A Numerical Investigation

A novel method to improve the robustness of steel end plate connections is presented in this paper. Existing commonly adopted techniques alter the stiffness of the beam or the end plate to improve the connection’s robustness. In this study, the robustness is enhanced by improving the contribution of the bolts to the rotational capacity of connections; the higher the bolts’ elongation, the higher the rotational capacity that can be achieved. However, the brittleness of the bolt material, combined with its small length, results in negligible elongation. Alternatively, the load path between the end plate and the bolts can be interrupted with a ductile element to achieve the required elongation. This can be achieved by inserting a steel sleeve with a designated length, thickness, and wall curvature between the end plate and the washer. The proposed sleeve should be designed so that its ultimate capacity is less than the force in the bolt at failure; accordingly, the sleeve develops a severe bending deformation before the failure of any connection components. Using a validated finite element model, end plate connections with various parameters are numerically investigated to understand the performance of the sleeve device. The proposed system substantially enhances the rotational capacity of the connections, ranging between 1.37 and 2.46 times that of the standard connection. It is also concluded that the sleeved connections exhibit a consistent elastic response with the standard connections, indicating the proposed system is compatible with codified elastic design approaches without modification. Furthermore, for a specific connection, various ductile responses can be achieved without altering the connection capacity nor configuration.

Experimental Study on Seismic Behavior of Precast Frame Columns with Vertical Reinforcement Spliced with Grouted Sleeve Lapping Connectors

Grouted splice connector is widely employed in precast concrete structures, but its utilization is still limited by shortcomings such as high construction cost, inconvenience in assemblage, and uncompacted grout caused by its small sleeve diameter. The grouted sleeve lapping connectors proposed by the authors can not only provide reasonable force transfer and convenient construction processing but also have the characteristics of low price and easy grouting. In this paper, the seismic performance of two full-scale precast concrete columns with two types of grouted sleeve lapping connectors was investigated, where type-I connector connected two lapped rebars and type-II connector connected four lapped rebars by a steel sleeve, respectively. A cast-in-situ column was also tested as a reference. All the specimens were tested under reversed cyclic horizontal load with a constant axial force. The distribution of cracks, failure modes, loading capacities, deformation abilities, stiffness, ductility, hysteresis loops, and energy dissipation of the specimens were studied. The type-I and type-II grouted sleeve lapping connectors satisfactorily transferred the stress of rebars when the columns reached their ultimate loads, and the seismic performance of the precast concrete columns was found to be comparable to that of the cast-in-situ column. Thus, the grouted sleeve lapping connector has a potential to replace the grouted splice connector in cast-in-situ connection.

Approximate estimation of the critical diameter in Koenen tests

A simple correlation between computed detonation parameters and the critical diameter obtained using the Koenen (steel-sleeve) test is reported. This correlation is not meant to replace a proper Koenen test, but rather, to act as an aid to help to know which orifice diameter to start testing with.

Numerical Analysis on Reinforcement Range of a Closed Steel Sleeve against Collapse

Before the shield machine begins to excavate, the end of the station structure often requires extensive soil reinforcement to ensure construction safety. Closed steel sleeve can prevent water leakage, sand leakage, and cave door collapse by balancing the water and soil pressure on the tunnel surface, thereby reducing the reinforcement range. In this study, a launching project of a closed steel sleeve is investigated; the Madis GTS finite element analysis software is used to simulate the triple-tube high-pressure jet-grouting pile to reinforce the water-rich sand layer. Soil displacement and stress after opening of the tunnel door are studied in detail at different longitudinal reinforcement lengths and transverse reinforcement scopes. The results show that, as the longitudinal reinforcement length increases, the displacement of the soil shows a decreasing trend, and the greater the length of the reinforced soil, the smaller the reduction in displacement. Furthermore, with the decrease of the lateral reinforcement range, though the soil settlement area has increased, the displacement remains unchanged. However, changing the end reinforcement range has no effect on the soil stress. In general, based on the strength and stability of the soil after the gate is cut out, the reinforcement range of the closed steel sleeve can be appropriately reduced compared to traditional reinforcement methods.