NUMERICAL ANALYSIS AND EVALUATION OF EFFECTIVE SLAB WIDTH OF COMPOSITE CONTINUOUS BEAMS WITH SEMI-RIGID JOINT

The characterization of the structural behavior of composite beams is directly affected by the determination of the effective slab width. Various codes propose their own definitions of the effective width based on the beam span and the slab width parameters. However, the evaluation of the effective width may be influenced by other parameters. The aim of this work is to determine the most important factors affecting effective width for continuous composite beams with semi-rigid joints using numerical simulations. A three-dimensional finite element model of a composite continuous beam using explicit-solver available in ABAQUS is developed. The proposed model is validated through comparisons to available experimental results. A modified model is proposed based on the so-validated model to study the influence of the composite beam-column joint stiffness on the effective width. Then, both numerical models are used to perform an extensive parametric study to investigate the influence of various parameters on the estimation of the effective slab width. The influence of slab width, the shear connection degree, and composite joint stiffness are particularly analyzed to find out the most important parameters influencing the effective width so that simplified equations for the calculation of the effective slab width are proposed.

Numerical Simulation and Parametric Analysis of Precast Concrete Beam-Slab Assembly Based on Layered Shell Elements

Precast concrete (PC) plays an important role in the industrialization processes of buildings, so it is critical to study the seismic performance of such structures. Several experimental and numerical studies have been conducted to investigate the behavior of PC beam-to-column connections. However, most of the previous studies neglect the contribution of slabs. In light of this, this paper presents a numerical simulation method for dry connected beam-slab assemblies based on the layered shell element available in OpenSees. The beams were modeled with fiber elements, while the slabs were modeled with layered shell elements. The developed model was validated by simulating a typical beam-slab assembly test, with the characteristics of hysteretic performance found to be well reflected by the model. Moreover, a parametric study was performed to quantify the influence of slab parameters. The results showed that the thickness of the slab had a significant effect on the hysteretic performance of the specimen and that the influence of the slab width was obviously reduced after it exceeded a certain limit. Besides, the effect of the reinforcement ratio on stiffness and loadbearing capacity was not obvious and was accompanied by a slight positive correlation with the energy dissipation capacity.

Theoretical Study on Prestress Loss in Cross-Tensioned Concrete Pavement with BFRP Tendons

Cross-tensioned concrete pavement can reduce transverse joints and cracks and improve the durability of the pavement, and the decrease in slab thickness can be achieved without damaging the performance of the pavement. However, the corrosion of the steel can cause serious damage to the pavement structure, resulting in higher maintenance costs and shorter service life. Basalt fiber-reinforced polymer (BFRP) has been proven to be an effective alternative in both jointed plain concrete pavement (JPCP) and continuously reinforced concrete pavement (CRCP) due to its lightweight and corrosion-resistant properties. In this paper, a systematic theoretical method for determining the prestress loss of BFRP tendons in cross-tensioned concrete pavement was proposed, with the impact of the slab width and distribution angle of the prestressed tendon on the prestress loss being studied and compared to the results of traditional steel strands. Results showed that the proportion of the prestress loss due to anchorage deformation and prestress retraction in the prestressing stage rose with the increase in distribution angle and the decrease in slab width, while the prestress loss during the in-service stage was a constant value for both BFRP tendons and steel strands. The prestress loss of BFRP tendons was far lower than that of steel strands in both prestressing stage and in-service stage for a given slab width (3 m, 4.5 m, 9.0 m, 12.75 m) and distribution angle (20°, 25°, 30°, 35°, 40°, 45°), and the difference ranged from 6.4% to 16%, signifying the feasibility of BFRP tendons in cross-tensioned concrete pavement. Overall, the smaller the slab width, the greater the difference of the prestress loss between BFRP tendons and steel strands.

Mantle plume dynamics at the rear of a retreating slab

SUMMARY In this paper, we present 3-D numerical simulations in which a compositional mantle plume rises through a shallow mantle layer at the rear of a retreating slab. The slab–plume buoyancy flux ratio Bs/Bp is varied from 3 to 30 over nine slab–plume simulations. The plume causes an overall decrease of the slab retreat rate from 15 to 7 % in the corresponding range $B_s/B_p=[3,30]$. The retreat rate decrease occurs in two stages: the first decrease occurs remotely when plume and slab are hundreds of kilometres apart; the second decrease is linked to the slab–plume-head impact. Continuous tracking of key positions along the plume head and conduit together with velocity profiling further shows a very close interplay between the conduit and plume head dynamics. In particular, the combination of the slab– and plume(head)–induced flows at the rear of the slab increases the advection and tilt of the conduit and causes its flaring with height in the direction parallel to the trench. As a result, the conduit source slowly drifts away from the slab by hundreds of kilometres and flares by one and a half times its original radius over 30 Myr of plume head spreading. The conduit tilt and flaring result in an increasingly unbalanced azimuthal distribution of the incoming plume flux from the feeding conduit into the head. These changes in the feeding conditions coupled with the mantle flow at the level of the plume head lead to the asymmetric spreading of plume material beneath the plate in the preferential direction that is parallel to the trench. Upon its arrival against the slab, it can be a front of buoyant material set to subduct along the slab width that has widened up to two and a half times its initial dimension. In nature, it is expected to extend from hundreds to thousands of kilometres depending on the slab–plume buoyancy flux ratio. To our knowledge, this study is the first to highlight the inter-relationships between a plume head and its feeding conditions in the plume source region.

Numerical analysis of local heat flux and thin-slab solidification in a CSP funnel-type mold with electromagnetic braking

In this article, based on the actual monitored temperature data from mold copper plate with a dense thermocouple layout and the measured magnetic flux density values in a CSP thin-slab mold, the local heat flux and thin-slab solidification features in the funnel-type mold with electromagnetic braking are analyzed. The differences of local heat flux, fluid flow and solidified shell growth features between two steel grades of Q235B with carbon content of 0.19%C and DC01 of 0.03%C under varying operation conditions are discussed. The results show the maximum transverse local heat flux is near the meniscus region of over 0.3 m away from the center of the wide face, which corresponds to the upper flow circulation and the large turbulent kinetic energy in a CSP funnel-type mold. The increased slab width and low casting speed can reduce the fluctuation of the transverse local heat flux near the meniscus. There is a decreased transverse local heat flux in the center of the wide face after the solidified shell is pulled through the transition zone from the funnel-curve to the parallel-cure zone. In order to achieve similar metallurgical effects, the braking strength should increase with the increase of casting speed and slab width. Using the strong EMBr field in a lower casting speed might reverse the desired effects. There exist some differences of solidified shell thinning features for different steel grades in the range of the funnel opening region under the measured operating conditions, which may affect the optimization of the casting process in a CSP caster.

Forward recursion approach of electromagnetic wave propagation characteristics in a slab of inhomogeneous magnetoplasma

Propagation characteristics of electromagnetic radiation incident on an inhomogeneous magnetoplasma slab near a good conducting metallic surface is investigated. The inhomogeneous plasma slab is divided into thin layers (sub-cells) in order to allow for treating each plasma sub-cell as a homogeneous medium. A global matrix is formed upon matching the fields at all interfaces, which allows for the analytical determination of the reflection, absorption and transmission coefficients. For matching the tangential fields at the metallic surface, an impedance (Leontovich) boundary condition has been used. Propagation characteristics are calculated numerically for a set of parameters that may be suitable for many applications including stealth plasma. Numerical results show resonant absorption peaks near the electron cyclotron frequency that increase by increasing the equilibrium plasma density. They also show absorption enhancement by increasing the plasma slab width.

Nonlinear surface waves propagating along the composite waveguide consisting of self-focusing slab between defocusing media separated by interfaces with nonlinear response

The model of the composite symmetric waveguide consisting of self-focusing slab between defocusing nonlinear media separated by interfaces characterized by own nonlinearity response is proposed. Two new types of nonlinear surface waves propagating along it with anti-phase amplitude oscillations at interface planes are found. The frequencies of the nonlinear surface waves existing near the interfaces with the nonlinear response only are calculated analytically. The conditions of the surface wave existence are found. The frequencies and localization distances of the surface waves in dependence on nonlinearity waveguide parameters, slab width and interface characteristics are analyzed.

Experimentelle Untersuchungen zum Einfluss der Bauteilbreite und der Schubschlankheit auf die Querkrafttragfähigkeit von Stahlbetonplatten ohne Querkraftbewehrung/Experimental Investigations on the Influence of the Slab Width and the Moment-Shear-Ratio on the Shear Capacity of RC Slabs without Shear Reinforcement

Trotz jahrzehntelanger Forschung ist die Frage nach dem Querkrafttragverhalten von Stahlbetonbauteilen bis heute nicht abschließend geklärt. Nach aktueller normativer Regelung wird bei der Bemessung grundsätzlich zwischen Nachweisen für Bauteile mit und ohne Querkraftbewehrung unterschieden. Während balkenförmige Bauteile stets eine Mindestquerkraftbewehrung aufweisen müssen, dürfen Stahlbetonplatten ohne Querkraftbewehrung ausgeführt werden. Der semi-empirische Querkraftbemessungsansatz nach EC 2 für Bauteile ohne Querkraftbewehrung wurde jedoch an einer Datenbank mit balkenförmigen Versuchskörpern hergeleitet, die überwiegend als gelenkig gelagerte Einfeldträger getestet wurden. Ein möglicherweise tragfähigkeitssteigernder Einfluss infolge einer großen Bauteilbreite wird dementsprechend nicht berücksichtigt. Weitere Einflüsse, beispielsweise infolge statischer Systeme, die vom gelenkig gelagerten Einfeldträger abweichen, werden bei der Bemessung ebenfalls nicht berücksichtigt. Anhand von Querkraftversuchen an Stahlbetonplatten, die über ihre gesamte Versuchskörperbreite belastet wurden und Referenzversuchen an schmalen Plattenstreifen, soll der Einfluss einer Plattentragwirkung auf die Querkrafttragfähigkeit untersucht werden. Durch variierende statische Systeme und Momenten-Querkraftverhältnisse (Schubschlankheiten) wird im Rahmen der Versuche sukzessive die Lage des Momentennulldurchgangs verändert, um verschiedene Lastabstände zum Innenauflager durchlaufender Systeme zu untersuchen. Dadurch soll der tragfähigkeitssteigernde Einfluss kleiner Schubschlankheiten quantifiziert werden.