Civil Engineering Design最新文献

This paper deals with the phenomenon of flattening or inflation of cross-sections caused by pure bending on beams of hollow circular cross-section with or without initial curvature. Both initially straight and initially bent tubes are analyzed under in plane bending. Results over a wide range of initial curvature values are presented. Finally, the area of validity of the expressions used is studied, as well as the deformations and stresses that occur in practice.

The goal of this work is to develop a complete theoretical framework for the numerical modeling of three-dimensional prestressed reinforced concrete structural members, soil mixture, and their interactions. This numerical formulation is based on the construction of a new composite finite element, in order to tackle the multi-scale problem. For this purpose, the mechanical behavior of each microstructure component material will be modeled as follows: (a) for the plain concrete (PC) and the soil mixture, an anisotropic-damage-elastoplastic model equipped with the strong discontinuity approach will be taken into account; (b) a polycrystal plasticity model, for the steel rebars and prestrssed tendons will be captured through a new strategy solution of discontinuous bifurcation problem, with the main objective to represent the multi-cracking phenomenon; (c) regarding the mechanical behavior of the aggregates and rocks (skeleton—hydro mechanic problem) in the PC and soil mixture, respectively, an anisotropic-damage-double-poro-polycrystal plasticity model equipped with softening material will be considered. An advanced failure algorithm based on the marching tetrahedron and the pseudo-termic problem will be developed. Finally, the zone that characterizes the interaction between the structural member and the soil mixture will be encrusted inside the composite finite element.

As the world population keeps growing, so does the demand for new construction. Considering material resources are limited, it will be unfeasible to meet such demand employing conventional construction methods. A new resource-saving approach is provided by adaptive structures. Using sensors, actuators and control units, structures are enabled to adapt to loads, for example, to compensate for deformations. Since deformations are dominant in the design of bending-stressed load-bearing structures, adaptivity enables such structures to be realized using less material and achieving the same load-bearing capacity in comparison to conventional designs. This article presents a concrete beam of typical building dimensions that compensates deflections by means of integrated fluidic actuators. These actuators offer the possibility of reacting optimally to general loading. The investigation is carried out on an approximately 4-m-long beam with integrated hydraulic actuators. To ensure the overall functionality, accurate dimensioning of the beam as well as the hydraulic system is mandatory. Analytical design of the beam and actuation system are carried out for predimensioning. Experimental testing validates the function and demonstrates that the adaptive beam works as predicted. A fully compensation in deflection is possible. Therefore, a significant increase in load-bearing capacity is possible with the same material input compared to conventional beams.

Glued-in rods are a class of adhesively bonded joints for timber engineering applications resulting in high-strength and stiffness connections. However, the use of polymeric adhesives may lead to issues related if the temperatures exceed their glass transition temperature, restricting their performance under quasi-static, or more critically, sustained loads. To overcome these, the substitution of polymeric adhesives by mineral high-performance grout was investigated. It was found that primers have neither a significant effect on strength nor on the failure mode; threated wood surfaces, however, resulted in a significant improvement of the latter. Based thereupon, grouted-in rods were manufactured. The best performance was achieved with a threaded wood surface, which achieved roughly 50% of the strength comparable adhesively bonded glued-in rod's strength. While the obtained strength may seem quite low, it is important to remind that the latter will largely remain unaffected by temperature; accordingly, made at room temperature, the comparison between grouted and glued rods is in favor of adhesive bonding, it may well be different at elevated ones.

The pursuit for more load-adapted, individualized, and at the same time precise building geometries is driving innovation in digital fabrication with concrete towards greater formal freedom and higher degrees of prefabrication. This article reviews the opportunities of using three-dimensional (3D)-printed formwork in the context of pre-fabricated concrete construction. It identifies the geometric specificities future planning tools need to address to incorporate the steps of modularization and fabrication into automatized planning processes from design to production. By reviewing the state-of-the-art fabrication methods for nonstandard concrete geometries, we highlight possible applications and challenges for additive formwork and introduce a volumetric modeling approach to modularize surface and mesh-based 3D design models into solid segments that can form the basis for further formwork planning.

Concrete is considered to be durable in permanent contact with water, making it a preferred material for the construction of drinking water reservoirs. More severe conditions, however, such as contact with purified water lead to the leaching of calcium and the deterioration of concrete surfaces. Due to the diffusive nature, deterioration begins superficially and ingresses with time. Consequently, concrete surfaces are severely damaged and the rebar-protective alkalinity can be lost. In this study, results from long-term laboratory leaching experiments in purified water of differently prepared concrete surfaces relevant for drinking water reservoirs are reported. Samples are monitored by both conventional laboratory techniques and, for the first time, by single-sided ¹H nuclear magnetic resonance to gain knowledge on appearance and performance as well as the microstructural changes with sub-millimeter depth resolution. Results give a deepened insight into the time- and depth-depending material changes. Concrete with a lower w/c ratio, more durable cement, or a densified surface shows a slowed deterioration. The progressing leaching deterioration is described using a combined diffusion-erosion model that allows a more direct comparison of results to other exposures.

Limiting crack widths to an acceptable level and determining the required minimum reinforcement are important tasks in the design of reinforced and prestressed concrete structures. Experience with different types of structures, ranging from watertight concrete structures to prestressed concrete bridges, shows that the concept currently applied in Germany and Austria is very effective and that significant changes are not necessary. The current draft for the revision of the EC2 (prEC2), however, presents a new concept for crack width verification and minimum reinforcement. In contrast to the concept currently used in Germany and Austria, this new concept is based more on the analysis and good reproduction of observations made in laboratory experiments and takes less account of the mechanical relationships of reinforced or prestressed concrete after cracking. For this purpose, numerous empirical factors are introduced which not only complicate the understanding but also the application in practice. However, an improvement in the accuracy of the crack width prediction is not achieved and the minimum reinforcement is significantly underestimated, especially for prestressed cross sections and thick members. In this article, the new concept set out in prEC2 is explained in detail. Its main weaknesses and contradictions are discussed by a comparison with the concept currently applied in Germany and Austria as well as detailed analysis of 2D FEM simulations with discrete cracks and adequate regard of the bond stress-slip relationship at the reinforcement-concrete interface. This should provide the basis for a factual discussion before the introduction of prEC2 into practice.

Drop tower tests on beam specimens were carried out to evaluate the influence of different geometric features and different loading velocities on the beams' response. Tested geometric characteristics are stirrup reinforcement in addition to longitudinal reinforcement, and notches. The goal is to quantify the differences in the global behavior and the amount of strains and strain rates measured at different positions on the reinforcement. This gives an insight into strain distributions along the rebars from which bond stresses can be derived. It can be stated that stirrup reinforcement kept the specimens together and thus increased the impact resistance. That was seen in the deflection and acceleration measurements, but it was also suggested by strain measurements, especially looking at residual strains. The maximum strains are generally more affected by global bending of the specimens than by the formation of a localized punching cone, which was the main failure mode.

The strong hygroscopic behavior of wood can lead to severe moisture-induced swelling deformations, especially perpendicular to the grain direction. Fully threaded screws arranged in this direction can be used as reinforcement and to constrain those deformations. Depending on the wood moisture content increase, tensile stresses in the screws and compression stresses in the surrounding solid wood evolve. A sufficiently accurate prediction of the maximum stresses occurring is important for reliable structural designs. For this reason, moisture-induced swelling experiments for two different configurations of screw diameter and specimen dimensions were performed within this work. Due to its homogeneity and its high swelling rate perpendicular to the grain, beech laminated veneer lumber (LVL) was used. A moisture content increase from oven-dry to about 7% led to screw tensile stresses in the magnitude of the yield strength and to highly nonlinear effects in the surrounding wood material. By means of a two-dimensional finite-element-based numerical simulation model, taking into account orthotropic plasticity and moisture-dependent material properties, the experiments could be simulated with high accuracy. The numerical results agree well with experimental observations. Based on a small parameter study, new insights into the complex interaction behavior between beech LVL and fully threaded screws could be gained.

Timber-concrete composite (TCC) ceilings build on the idea of making use of the advantageous properties of both materials symbiotically. While concrete, as the upper layer, is used to absorb the compression forces, wood is used in the lower layer to absorb the tensile forces. Many systems have been developed with special attention paid to solutions with both a continuous concrete and wood layer. This article introduces a new system developed with the primary focus set on the most efficient material use by introducing a free space between the concrete and the wood layer using special vault shaped moldings. The first part of the paper contains an introduction including a short overview of different embodiments of TCC floor systems. The second part focuses on the design of the new system and gives an overview of the estimated structural performance. In the third part the environmental performance of the new system is discussed in comparison to chosen existing systems focusing at the the whole life-cycle including a re-use (A-D).