AbstractA new concept has been developed for connecting spread footings and precast columns in bridges. The socket connection is constructed by precasting the column, erecting it, and casting the ...reinforced concrete footing around it. This system saves construction time on site because, in little more than the time needed to construct the footing, both the column and footing can be constructed. Site erection is facilitated by the fact that the field tolerances are essentially unlimited. The longitudinal column bars are straight and are terminated with mechanical anchors. This arrangement improves constructability, because no bars cross the interface between the column and footing, and it provides better transfer of forces in the connection region than is possible with conventional bent-out longitudinal bars. The surface of the column is roughened to improve adhesion to the surrounding cast-in-place concrete. Axial-load tests demonstrated that the connection can resist column axial loads far above those expected in practice. Cyclic, lateral-load tests demonstrated that the seismic performance of the connection is at least as good as, if not better than, that of a comparable cast-in-place system. The recent deployment of the new system in a highway overpass provided both field experience and initial estimates of the potential time savings.
•A new connection detail for concrete filled steel tubes to footing was tested.•Load transfer mechanism consists of shear connectors and dowel bars embedded in UHPC.•The mode of failure varied based ...on the connection detail used.•The capacity protected element did not suffer damages.
Concrete filled steel tubes (CFSTs) provide improved structural strength and ductility in addition to eliminating the need for column formwork. This research proposes new connection details for column-to-footing connection using ultra-high performance concrete (UHPC). Two connections consisting of an embedded and an encased layer of UHPC were selected for the experimental program. In these details, the CFST is embedded in a layer of UHPC located near the plastic hinge zone of the column and steel dowels from the footings are used for force transfer. The sequence of construction and detailing allows the use of these connection details for accelerated bridge construction (ABC) applications. Two columns were tested under a combination of constant axial and incremental cyclic lateral load. The embedded type connection failed by fracture of the tube while the encased type connection induced damages in the UHPC encasement. Both connections exhibited high levels of ductility and did not show significant loss of lateral load capacity. The load hysteresis of the embedded connection showed higher energy dissipation for the embedded connection when compared to the encased connection due to damages in the UHPC encasement. The capacity protected footing did not show any signs of cracking.
Greg Johnson, Administrator for the Interstate Bridge Replacement Program, joins the ITE Talks Transportation podcast to discuss the ins and outs of this $6 billion project spanning the Columbia ...River and connecting the US states of Washington and Oregon. The project is replacing a 106 year-old bridge on I-5, the only West Coast interstate in the US that goes from Canada to Mexico. Johnson talks about the complexities of managing a large infrastructure project, what it's like working with two state DOTs, and the importance of engaging community members and having buy-in for this multimodal project. He also highlights the equity considerations involved in the project and how data is being utilized to ensure equitable and inclusive outcomes for the communities touched by the Interstate Bridge Replacement Program.
The first highly diastereoselective TfOH-catalyzed Michael addition/N,O-ketalization sequence of 3-aminooxindoles and ortho-hydroxychalcones was achieved, delivering a wide range of bridged cyclic ...N,O-ketal spirooxindoles with complex and strained structures in 41-97% yields. Moreover, a gram-scale experiment and some chemical conversions were conducted to further demonstrate the synthetic value.
In this contribution, we combine density functional theory (DFT) calculations, experimental kinetic study and DFT-assisted analysis to elucidate the impact of the interface of monolayer Pt on the Ni ...surface on catalytic performance of steam methane reforming including carbon formation on core-shell (Ni@Pt) catalysts and compare it with Ni and Pt catalysts. We demonstrate that core-shell structured Ni@Pt significantly lowers the carbon formation without sacrificing much the activity. The DFT results demonstrate that the metal identity, core shell structure and support have significant impacts on the reaction mechanisms. The direct methane activation is energetically favorable reaction pathway on Ni, while the OH* assisted methane activation is the favorable pathway on Pt and Ni@Pt catalysts, where methane activation is the rate-determining step on all catalysts. We unambiguously reveal that the core-shell Ni@Pt catalyst modified the surface Pt electron density and shifted d-band center away from Fermi level compared to Ni(1 1 1) and Pt(1 1 1). It results in a strong basic surface OH* which actively reacts with CHx and thus enhances carbon formation resistance. Above all, Ni-core/Pt-shell particle could decouple the activity and carbon resistance to keep the activity and reduce carbon formation simultaneously in methane steam reforming. In addition, by taking into account the activation of steam on the support, the effective activation energy estimated from DFT-assisted analysis is well consistent with the experimental value on the both Ni and Ni@Pt catalysts, which could shed some light on building a bridge between experimental work and DFT-assisted kinetic study.
‘Sustainability’, ‘circular economy’, ‘circular construction’ have received increasing attention in the last decade. However, their interpretation is often unclear, as is the way a certain study fits ...into these research fields. In this paper, therefore, first a definition of both ‘sustainability’ and ‘circular economy’ is proposed. It is concluded that sustainability is the goal, while the circular economy is a means to achieve a more sustainable economy.
Subsequently, the application of the circular economy in the construction industry is investigated, with a special focus on bridge construction. Reason is that, for instance, many concrete pedestrian bridges currently find themselves in the end-of-life phase, are demolished and often merely rebuilt, with a lot of material and energy loss as a consequence. An investigation of the available circular construction principles is therefore performed in order to determine certain limitations and gaps for future research and to stipulate the path to be followed towards circular bridge construction. This is necessary in order to prevent the same cycle of demolition and replacement from being run through again in a few decades.
It is concluded that the meso-scale, the construction in general, is rarely discussed. Yet, an in-depth investigation is necessary in order to develop specific design strategies for circular bridges. A certain standardisation scheme to facilitate circularity, needs to be developed. This scheme should, however, still allow enough architectural freedom. Additionally, this scheme needs to be accompanied by, to be developed, meso-scale circularity indicators to effectively assess the eventual circularity of a bridge.
•Sustainability is the goal, circular economy is the means to this end.•Specific design strategies for circular bridge construction are to be developed.•The meso-scale, the construction, needs to be elaborated thoroughly.•Circularity assessment requires a different approach from sustainability assessment.
This paper explores a proof of concept self-centring spinal column concept experimentally. The idea of the system is inspired by the mechanical interaction of the vertebral bones and intervertebral ...discs in human spine. Experimental tests are undertaken to explore whether a similar bridge pier system could be constructed to withstand seismic dynamic loading in an equally efficient manner. The experimentation is performed on tied (pre-tensioned) wooden blocks (vertebrae) with and without rubber strips between the vertebrae acting as the intervertebral discs. Small-scale test specimens are excited sinusoidally using a small-scale shake table, and the response of the system recorded through triaxial accelerometers attached to the structure. The nonlinear dynamic response and mechanics of the system are then investigated under sinusoidal dynamic excitation. It is found that the integration of intervertebral rubber discs into wooden vertebrae reduces the nonlinearity of the system, and increases the flexibility and damping. The experimental results show that the proposed system can sustain large lateral displacement without any residual deformation after the excitation.
A strategically novel single C-F bond functionalization of CF
3
-derived molecules, which shows a prominent advantage for the expedient construction of difluoromethylene-bridged organic scaffolds, is ...disclosed. The reported protocol consists of S
N
2′ amination,
N
-alkylation and palladium-catalyzed allylic substitution reactions, which enables straightforward arylation and alkenylation of vinyltrifluoromethane derivatives. Furthermore, this strategy is characterized by its broad substrate scope with respect to both CF
3
-alkene and arylboronic acid derivatives.
Through an S
N
2′ amination,
N
-alkylation and palladium-catalyzed allylic substitution sequence, we realized
ipso
-C-F bond arylation/alkenylation of trifluoromethylalkene derivatives.
Display omitted
•The central concept of 3D concrete printing was described.•A novel fly ash based geopolymer mortar was formulated for large scale concrete printing application.•Fresh and hardened ...properties were characterized for printability of geopolymer mortar.•Tensile bond strength of the printed geopolymer was evaluated with respect to printing parameters.
The structural capacity of construction joints in concrete bridges, deck and pavements mainly depends on the bond strength between the old substrate and new overlaid concrete. Sometimes, a mismatch in the properties of old and new concrete may lead to early age failure and shortened service life. Since in 3D concrete printing (3DCP), the whole object is made by layer by layer, bond strength is considered as one of the key parameters to ensure stability in the structure. For understanding bond mechanism, it is essential to measure bond strength at the interface between new and old layer and investigate significant parameters affecting this property. In this direction, our current work targets to analyse tensile bond strength of 3D printed geopolymer mortar with respect to printing time gap between layers, nozzle speed and nozzle standoff distance. A novel formulation of fly ash based geopolymer was made and printed using four-axis automated gantry system. Experimental findings reveal that the bond strength is a function of state of interface material between two nearby layers which can be influenced by material strength development rate and 3D printing parameters.
The complexity and uncertain nature of bridge construction projects require simulation for analyzing and planning these projects. On the other hand, optimization can be used to address the inverse ...relationship between the cost and time of a project and to find a proper trade-off between these two key elements. In addition, the large number of resources required in large-scale bridge construction projects results in a very large search space. Therefore, there is a need for using parallel computing to reduce the computational time of the simulation-based optimization problem. Another problem in this area is that most of the construction simulation tools need an integration platform to be combined with optimization techniques. To alleviate these limitations, an integrated simulation-based optimization framework is developed within one High Performance Computing (HPC) platform, and its performance is analyzed by carrying out a case study. A master-slave (or global) parallel Genetic Algorithm (GA) is used to decrease the computation time and to efficiently use the full capacity of the computer. In addition, sensitivity analysis is applied to identify the promising configuration for GA and the best number of cores used in parallel and to analyze the impact of GA parameters on the overall performance of the simulation-based optimization model. Using NSGA-ΙΙ as the optimization algorithm resulted in better near-optimal solutions compared to those of fast-messy GA. Moreover, performing the proposed framework on multiple nodes using the cluster system led to 31% saving in the computation time on average. Furthermore, the GA was tuned using sensitivity analyses, which resulted in the selection of the best parameters of the GA.
•Integrating Discrete Event Simulation (DES) with GA multi-objective optimization•Solving time-cost construction problem using a simulation tool compatible with HPC•Tuning the optimization and finding the best number of cores used in parallel•Investigating the feasibility of the proposed framework through a case study
PDF
