Frontiers of Architecture and Civil Engineering in China

Các dầm bê tông gia cường bao gồm cả thanh thép và thanh polymer gia cường sợi thủy tinh cho thấy sức mạnh, khả năng phục vụ và độ bền tuyệt vời. Tuy nhiên, hiệu suất chịu cắt mỏi của những dầm này vẫn chưa rõ ràng. Do đó, các dầm với các thanh dọc và kích thước cắt hỗn hợp đã được thiết kế và thực hiện các thử nghiệm chịu cắt mỏi. Đối với các mẫu nghiệm thất bại do chịu cắt mỏi, tất cả các kích thước cắt bằng polymer gia cường sợi thủy tinh và một số kích thước cắt bằng thép đã bị gãy tại vết nứt chéo quan trọng. Đối với mẫu nghiệm thất bại qua thử nghiệm tĩnh sau 8 triệu chu kỳ mỏi, khả năng tĩnh sau mỏi không giảm đáng kể so với giá trị tính toán. Mức độ mỏi ban đầu có ảnh hưởng lớn hơn đến sự phát triển vết nứt và tuổi thọ mỏi hơn là mức độ mỏi trong giai đoạn sau. Sức chịu cắt mỏi của các kích thước cắt bằng polymer gia cường sợi thủy tinh trong các mẫu nghiệm có phần thấp hơn so với các thử nghiệm căng trục dọc trên thanh polymer gia cường sợi thủy tinh ở không khí và các thử nghiệm hàn nối trên thanh polymer gia cường sợi thủy tinh, và các chế độ thất bại là khác nhau. Các kích thước cắt bằng polymer gia cường sợi thủy tinh đã chịu tải mỏi và cắt, và thất bại do cắt.

Considering failures during machinery processes such as drilling, a precautionary analysis involving delamination and the corresponding dissipated energy is required, especially for composite structures. In this context, because of the complexity of both the analysis procedure and experimental test setup, most studies prefer to represent mode I and III interlaminar crack propagation instead of that involving mode II. Therefore, in this study, the effect of mode II delamination and corresponding interlaminar crack propagation was considered during the drilling process of multilayered glass/polyester composites using both numerical and experimental approaches. In the experimental procedure, the mechanical properties of the glass/polyester specimens were obtained according to ASTM D3039. In addition, the interlaminar mixed-mode (I/II) loadings were determined using an ARCAN test fixture so that the fracture toughness of glass/polyester could then be identified. The mode II critical strain energy release rate (CSERR) was then obtained using an experimental test performed using an ARCAN fixture and the virtual crack closure technique (VCCT). It was determined that the numerical approach was in accordance with the experiments, and more than 95% of crack propagation could be attributed to mode II compared to the two other modes.

The aging structure as well as the considerable increase of heavy-traffic load on Germany’s motorways and trunk roads encourages the use of innovative, sound and reliable methods for the structural assessment on network level as well as on project level. Essential elements for this are data, which allow a reliable assessment. For a holistic approach to structural pavement assessment performance orientated measurements will be necessary. In combination with functional parameters as well as write-down models, strategically motivated decision making processes will be useful combined with technically motivated decision processes. For the application at the network level, the available methods for performance orientated measurements are still challenging, as they are based either on testing drill-cores or on nontraffic speed methods. In recent years significant innovation steps have been made to bring traffic speed bearing capacity measurements and methods for evaluating pavement structures on the road. The paper summarizes the actual assessment procedures in Germany as well as the ongoing work on the development and implementation of new methods and techniques.

Prefabricated internal structures of road tunnels, consisting of precast elements and the connections between them, provide advantages in terms of quality control and manufacturing costs. However, the limited construction space in tunnels creates challenges for on-site assembly. To identify feasible connecting joints, flexural tests of precast straight beams connected by welding-spliced or lap-spliced reinforcements embedded in normal concrete or ultra-high-performance fiber-reinforced concrete (UHPFRC) are first performed and analyzed. With an improvement in the strength grade of the closure concrete for the lap-spliced joint, the failure of the beam transforms from a brittle splitting mode to a ductile flexural mode. The beam connected by UHPFRC100 with short lap-spliced reinforcements can achieve almost equivalent mechanical performance in terms of the bearing capacity, ductility, and stiffness as the beam connected by normal concrete with welding-spliced reinforcements. This favorable solution is then applied to the connection of neighboring updeck slabs resting on columns in a double-deck tunnel. The applicability is validated by flexural tests of T-shaped joints, which, fail in a ductile fashion dominated by the ultimate bearing capacity of the precast elements, similar to the corresponding straight beam. The utilization of UHPFRC significantly reduces the required lap-splice length of reinforcements owing to its strong bonding strength.

A theoretical solution is aimed to be developed in this research for predicting the failure in internally pressurized composite pressure vessels exposed to low-velocity impact. Both in-plane and out-of-plane failure modes are taken into account simultaneously and thus all components of the stress and strain fields are derived. For this purpose, layer-wise theory is employed in a composite cylinder under internal pressure and low-velocity impact. Obtained stress/strain components are fed into appropriate failure criteria for investigating the occurrence of failure. In case of experiencing any in-plane failure mode, the evolution of damage is modeled using progressive damage modeling in the context of continuum damage mechanics. Namely, mechanical properties of failed ply are degraded and stress analysis is performed on the updated status of the model. In the event of delamination occurrence, the solution is terminated. The obtained results are validated with available experimental observations in open literature. It is observed that the sequence of in-plane failure and delamination varies by increasing the impact energy.

Roundabouts are becoming a preferred form of intersection control type due to their safety and capacity benefits. Yield control at roundabout entries inherently reduces fuel consumption and emissions when compared to other conventional intersection types. However, these benefits can be limited by poor driver behavior and judgment when entering the roundabout. This research addresses the nature of gap distributions and use of turn indicators by exiting vehicles at three single-lane roundabouts in Vermont, New York, and Alaska. Presented here is a comparison of vehicle headways measured at two different locations in each roundabout. Rejected headways are analyzed in the context of priority abstaining events when entering drivers yield to vehicles exiting on the same leg of the roundabout suggesting that “true” critical gaps are being overestimated. Results indicate that exiting vehicles, particularly those that do not use their turn indicators when departing from the major-stream of traffic have an influence on the entry decision of drivers on the same approach. This behavior is of particular concern for intersection efficiency (i.e., delay) and sustainability (i.e., excess fuel consumption and emissions). Results prompt the consideration of more consistent guidance on and enforcement of turn indicator use during roundabout negotiations.

A reasonable choice of structure of a model box is significant for a shaking table test to be successful in geotechnical engineering. A model box has been designed for the shaking table test of a subway station structure in the soft soil of Shanghai in the paper. The reasonable geometric similarity scale of the subway station structure has been determined by a 3-D dynamic analysis under the action of lateral equivalent static loading. The shape, size and structure of the model box are chosen by considering all the involved factors comprehensively. The shape of the box is similar to that of a typical station structure, and the ratio between the plane dimension of the model ground and that of the model structure is big enough to reduce the influence of boundary condition effectively. The structure is strong enough to avoid being demolished by shaking during a test. The contact conditions between the model soil and box are clear to help the data gained from the test well fit that from numerical analysis. The total weight of the model soil and box is less than the bearing capacity of the shaking table apparatus and there is no resonance between the model soil and box. The results show that the model box can be used to simulate the dynamic response of a subway station structure very well, so it provides a firm foundation for the success of the shaking table test of a subway station structure.

This paper investigates the staying and moving characteristics of office workers in a non-territorial office using an ultra wide band (UWB) impulse radio sensor network. The differences between office workers’ staying and moving are clarified according to the individual workstation type that they select. The study determines the characteristics of each type of workstation. By clarifying office workers’ preference for staying and moving with regard to individual workstation types and office worker post, the reasons why office workers in different posts tended to select different types of workstations were revealed. Specifically, leaders tended to select workstations at the “inner meeting corner side” most frequently, as they had a greater need to stay in other areas. In contrast, ordinary staff needed to visit office workers in other areas less often, and as such, they tended to select individual workstations at the “middle meeting corner side.” Barring this, they tended to select individual workstations at the “middle corridor side” or “outer-meeting corner side.” Temporary staff members had little need to visit or stay at other places so they tended to select individual workstations at the “window side,” which is seldom visited or stayed at by other office workers and they could be disturbed less often from their solo work.