Soil stabilization using Portland cement is a widely adopted technique. Previous research has demonstrated that molasses, which contains sugars, enhances the reaction between cement and aggregates. This study investigates the impact of adding molasses to soil stabilized with Ordinary Portland Cement (OPC) on geotechnical properties. Expansive clay soil samples from Taru Jabba, District Nowshera, Pakistan, were treated with various combinations of molasses and cement. The concentrations of each stabilizer were varied at 0%, 4%, 8%, and 12% by dry weight of the soil. Additionally, the soil was treated with constant molasses contents of 4%, 8%, and 12%, while varying the cement content at 4%, 8%, and 12% by dry weight. Geotechnical tests, including Proctor compaction, Atterberg limits, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and swelling potential, were conducted to assess the effects of the stabilizers. The results indicated that the addition of molasses improved soil strength, mitigated shrinkage cracks, and reduced brittleness. Specifically, the CBR value increased from 3.2% in the native soil to 12.3% with 12% molasses and 12% cement. The Plasticity Index (PI) decreased from 14.23% to 8.12%, and the CBR swell value reduced from 9.66% to 3.82%. Furthermore, the UCS of the stabilized soil increased by 64.7% compared to the untreated soil after a 7 day curing period.

Caisson foundations are commonly used as the tower foundations in many long-span bridges. However, the seismic performance analysis of bridge structures using caisson foundations typically assumes that the tower is fixed at the base, applying the free-field ground acceleration to the base. Consequently, the impact of soil–caisson dynamic interaction (SCDI) on the caisson foundation motion is not considered. To investigate the SCDI effects on the motion of the caisson foundation, two different systems of 1 g shaking table model tests were carried out: a free-field system model test and a soil–caisson system model test. The test results show that an increase in the peak acceleration of the table input seismic wave is associated with a greater influence of SCDI on the motion of the caisson foundation. Compared with the free-field ground motion, the SCDI effects reduce the amplitude of the horizontal acceleration of the caisson foundation motion but introduce a significant rotational component. Additionally, both effects are frequency-dependent and become more significant with increasing frequency. The shaking table test study presented in this paper reveals several crucial features of SCDI that influence the motion of the caisson foundation, enhancing the comprehension of the mechanism of SCDI and providing essential data support for subsequent theoretical and numerical simulation studies.

The use of U-shaped girders has become increasingly popular in advanced projects such as metro rail systems due to their ability to provide greater vertical clearance beneath bridges. These girders, characterized by two webs and a bottom flange, contribute essential longitudinal stiffness and strength to the overall structure while effectively countering torsional forces in curved bridges. However, the design and construction of U-shaped girders present challenges, including their relatively higher self-weight compared to other girder types. Consequently, cost optimization has become a crucial focus in structural design studies. This research aims to develop an optimization model for prestressed U-shaped girders using the AASHTO LRFD bridge design specifications. The model is based on the Box complex method, with necessary modifications and improvements to achieve an optimal design. The objective is to minimize the total cost of materials, including concrete, steel reinforcement, and prestressing strands, while satisfying explicit and implicit design constraints. To facilitate the analysis, design, and optimization processes, a program is developed using Visual Studio 2010 and implemented in Visual Basic (VB.NET). The program incorporates separate subroutines for analysis, design, and optimization of the prestressed U-shaped girder, which are integrated to produce the desired results. When running the program, the optimization process required 229 iterations to converge to the optimal cost function value. The results demonstrate that the developed algorithm efficiently explores economically and structurally effective solutions, resulting in cost savings compared to the initial design. The convergence rate of the moment capacity constraint is identified as a key factor in achieving the optimal design. This research makes a significant contribution to the field of civil engineering by applying the classical Box complex method to the optimization of girders, an area where its utilization has been limited. Furthermore, this study specifically addresses the optimization of prestressed U-shaped girders in metro rail projects, where they serve as both the deck and support structure for train loading. By employing the Box complex method, this research aims to fill the research gap and provide valuable insights into the optimization of U-shaped girders. This approach offers a fresh perspective on designing these girders, considering their unique role in supporting metro rail loads. By leveraging the benefits of the Box complex method, researchers can explore new possibilities and uncover optimal design solutions for U-shaped girders in metro rail applications.

In order to improve the post-earthquake resilience of bridge structures, a Two-Stage seismic isolation method is proposed in this paper. According to the method, the restoring force and horizontal stiffness are smaller in the first stage and become much larger in the second stage. Therefore, a new kind of seismic isolation device, Two-Stage Friction Pendulum Bearing (TSFPB for short), is invented based on the traditional friction pendulum bearing (FPB for short). In this paper, the geometry configuration, sliding states and hysteresis characteristics of the bearing are first introduced with a theoretical approach. Then the hysteresis curve of the TSFPB is verified experimentally and the simulation method of the bearing in an FEM software is proposed. Last, a numerical analysis for an actual highway girder bridge is carried out to compare the seismic design method recommended in this paper with the conventional seismic isolation method. It is found that the Two-Stage seismic isolation method has an adaptive restoring force, horizontal stiffness and energy dissipation mechanism for different seismic intensity levels and better seismic performance compared with a conventional seismic isolation method. In addition, bridges with TSFPBs have smaller residual displacements and better post-earthquake resilience than those with traditional FPBs.

Soil stabilization using Portland cement is a widely adopted technique. Previous research has demonstrated that molasses, which contains sugars, enhances the reaction between cement and aggregates. This study investigates the impact of adding molasses to soil stabilized with Ordinary Portland Cement (OPC) on geotechnical properties. Expansive clay soil samples from Taru Jabba, District Nowshera, Pakistan, were treated with various combinations of molasses and cement. The concentrations of each stabilizer were varied at 0%, 4%, 8%, and 12% by dry weight of the soil. Additionally, the soil was treated with constant molasses contents of 4%, 8%, and 12%, while varying the cement content at 4%, 8%, and 12% by dry weight. Geotechnical tests, including Proctor compaction, Atterberg limits, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and swelling potential, were conducted to assess the effects of the stabilizers. The results indicated that the addition of molasses improved soil strength, mitigated shrinkage cracks, and reduced brittleness. Specifically, the CBR value increased from 3.2% in the native soil to 12.3% with 12% molasses and 12% cement. The Plasticity Index (PI) decreased from 14.23% to 8.12%, and the CBR swell value reduced from 9.66% to 3.82%. Furthermore, the UCS of the stabilized soil increased by 64.7% compared to the untreated soil after a 7-day curing period.