We investigate how the mechanical properties of intra‐oceanic arcs affect the collision style and associated stress‐strain evolution with buoyancy‐driven models of subduction that accurately ...reproduce the dynamic interaction of the lithosphere and mantle. We performed a series of simulations only varying the effective arc thickness as it controls the buoyancy of intra‐oceanic arcs. Our simulations spontaneously evolve into two contrasting styles of collision that are controlled by a 3% density contrast between the arc and the continental plate. In simulations with less buoyant arcs (15–31 km; effective thickness), we observe arc‐transference to the overriding plate and slab‐anchoring and folding at the 660 km transition zone that result in fluctuations in the slab dip, strain‐stress regime, surface kinematics, and viscous dissipation. After slab‐folding occurs, the gravitational potential energy is dissipated in the form of lithospheric flow causing lithospheric extension in the overriding plate. Conversely, simulations with more buoyant arcs (32–35 km; effective thickness) do not lead to arc‐transference and result in slab break‐off, which causes an asymptotic trend in surface kinematics, viscous dissipation and strain‐stress regime, and lithospheric extension in the overriding plate. The results of our numerical modeling highlight the importance of slab‐anchoring and folding in the 660 km transition zone on increasing the mechanical coupling of the subduction system.
Plain Language Summary
Continents grow by the successive accretion of material to their margins, mostly collision and accretion of intra‐oceanic magmatic arcs. We investigate the effect of arc buoyancy and viscosity on the mode of collision, and the effects on the margin using a computer modeling approach. Our simulations show that upon collision, it is a small differential in density (3%) between the colliding arc and the continental margin that dictates whether subduction continues or stops after collision. In addition, our models show that arc buoyancy and viscosity drive lithospheric extension in the continental plate. Also, as the subducting slab reaches a mantle discontinuity at 660 km depth, it folds and causes strain and stress fluctuations on the margin.
Key Points
Arc‐continent collision can result in two contrasting styles of collision depending on the buoyancy of the weak intra‐oceanic arc
The mechanical properties of intra‐oceanic arcs decrease the mechanical coupling of the subduction system and drive extension in the overriding plate
Lithospheric‐deep mantle interactions increase the mechanical coupling of the subduction system and drive punctuated events of increased compression
Fire is one of the most severe conditions encountered during the lifetime of a structure. Consequently, the provision of proper fire safety measures for structural members is a major safety ...requirement in building design. In this paper an experimental study is reported on the axial deformation of GGBS-FA-SF blended geopolymer mortar and geopolymer concrete with and without steel fibre when they are subjected to both mechanical and thermal loadings. The transient tests were conducted in Instron machine with additional heating facility. During the test the specimen was first subjected to a pre-defined mechanical load and followed by thermal heating. The transient axial deformations of the tested specimens were recorded using digital image correlation camera. By using the experimentally obtained temperature-dependent thermal strains of the specimen with different preloads the transient strains of the geopolymer mortar and geopolymer concrete with and without steel fibre are analysed and evaluated. Finally, empirical formulas are also proposed to reproduce the influence of the preload, heating temperature and constituents of the mix on the transient strain of geopolymer mortar and geopolymer concrete.
•Experimental results are reported for thermal strains of free expansion of geopolymer concrete.•Experimental results are reported for thermal strains of prestressed geopolymer concrete.•Experimental results of transient strains of geopolymer concrete are reported.•Temperature- and prestress-dependent transient strain formulas are proposed.•The effect of coarse aggregate and steel fibre on transient strains is examined.
•Short-term creep and transient strain increases with increasing stress levels and higher temperature.•The evolution of free thermal strain below 150 ℃ is slow, however, a sharp increase was observed ...above it.•Heating rate have no prominent influence on transient strain of RPC.
Reactive powder concrete (RPC) shows a great application potential owing to its superior strength and excellent durability. However, creep behavior at high temperature is a major concern, as scanty information is available in the past literature. Therefore, the aim of this paper is to investigate the creep behavior of RPC at high temperature. Creep behavior is further segregated into free thermal strain, short-term creep and transient strain based on different thermo-mechanical regimes. Steady-state thermal and loading conditions and transient thermal and loading conditions were considered. Tests were carried out from 10 to 60% stress level of ambient and high-temperature compressive strength ratios and up to target temperature of 900 °C. The result shows that short-term creep of RPC increases considerably above 500 °C and the increase under the same loading ratios at 700 and 900 °C is approximately 13 and 23 times as that of short-term creep at 120 °C, respectively. Furthermore, increased stress level also triggered the short-term creep within the same target temperature. The evolution of free thermal strain and transient strain were slow below 250 °C. However, at higher temperature, the increase in strain rate becomes noticeable. It was found that heating rate has a direct influence on the expansion of RPC. On the other hand, transient strain was not affected by increasing heating rate from 3 to 5 °C/min. Finally, fitting equations were proposed which will be useful in fire safety design of RPC structures in computer programmes.
Concrete behaviour at high temperature was investigated in depth since the 1970s, in order to highlight the main issues linked to its mechanical performance in hot conditions, such as chemical ...processes, kinematic behaviour (transient and creep strains) and evolution of the physico-mechanical properties. Thanks to these studies, a few constitutive models have been proposed in the literature for concrete at high temperature, with the aim of modelling reinforced concrete structural behaviour during heating. Within this context, a Beam Finite Element code for thermo-mechanical analyses has been developed by using a Fortran solver and GID as pre- and post-processor. A number of well-documented full-scale tests on reinforced concrete columns exposed to Standard Fire (without cooling) was simulated numerically, by implementing four different constitutive models proposed in the literature for concrete at high temperature. The main goals are: to highlight the role of some critical aspects regarding reinforced concrete members in hot conditions, in particular second-order effects, transient and creep strains (a), and to make a systematic comparison between numerical and experimental results in order to assess the reliability of both 1D numerical modelling (b) and the adopted constitutive models for concrete (c). The results confirm that 1D numerical modelling is generally consistent with the experimental evidence if transient and creep strains, as well as second-order effects are carefully taken into account. Moreover, the differences among the four investigated models for concrete behaviour in compression are quite limited.
•The behaviour of columns under a standard fire can be adequately well described by beam finite elements.•There are no major differences between any of the explicit and implicit models.•The EC2 model allows the best agreement between experimental and numerical results.
Structural members experience significant creep deformations in later stages of fire exposure, and are susceptible to failure due to high-temperature creep effects. However, in current practice creep ...deformations are not fully accounted for in evaluating fire resistance. This paper presents an approach to account for high-temperature transient creep in evaluating fire resistance of reinforced concrete (RC) columns. A three dimensional finite element based numerical model is built in ABAQUS to trace the behavior of RC columns under fire. Temperature induced transient creep strains in concrete and reinforcing steel are explicitly accounted for in the analysis. The model also accounts for temperature induced degradation in concrete and reinforcing steel, and material and geometrical nonlinearities. The model is applied to evaluate the effect of high-temperature creep on the response of fire exposed RC columns. Results from the analysis clearly indicate that high-temperature transient creep significantly influence the extent of deformations when the temperatures in concrete exceed 500 °C, and this in turn influences failure time of RC columns. Thus, neglecting temperature dependent transient creep strains can lead to underestimation of predicted deformations and this can result in un-conservative fire resistance estimation in RC columns.
Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser ...welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa).
► The transient strain model of concrete under the biaxial stress state is proposed. ► A concept of the transient modulus is put forward. ► A failure criterion for determining the fire resistance of ...the slab is suggested. ► Three-stage response mode of the slab subjected to fire is revealed and simulated.
This paper proposes a transient strain model of concrete with a transient modulus under the biaxial stress state and a failure criterion for determining the fire resistance of two-way reinforced concrete slabs. A program was developed to calculate the three-stage response mode and fire resistance of such slabs. Unlike tests and past studies, this program verified the developed constitutive model of concrete and the necessity of including transient strain in the model. The parametric study included in this research further specified the influence of concrete’s thermal strain and steel’s creep strain on the behavior of the slab during fires.
Display omitted
Laser welding is considered as a promising way to suppress the softening problem of welded structures of high strength low alloy steel (HSLA) in quenched and tempered state. Mapping ...relation between joint strength and the minimum microhardness of the softened zone was established for fibre laser welded 6mm-thick HSLA joints, as well as that between welding speed and the minimum microhardness of the softened zone to facilitate the optimism of fibre laser welding process of 20MnTiB HSLA. By using a welding heat input as low as about 240kJ/m, the tensile strength of a fibre laser welded 6mm-thick 20MnTiB joint could be almost the same as the quenched and tempered base metal due to the low aspect ratio of the cross section of the softened zone (RSZ) formed in the heat affected zone (HAZ) of welded joint. The transient strain field and the damage evolution history were compared between softened zones with very different cross-sectional aspect ratio, aiming to get a better understanding of the effects of RSZ on the performance of as-welded 20MnTiB joint. The numerical studies were carried out to investigate the underlying mechanism of the effect of softened zone on the overall strength of the welded joint.
The Chaman fault in Western Pakistan marks the western collision boundary between the Indian and Eurasian plates and connects the Makran subduction zone to the Himalayan convergence zone. ...Geomorphic-scale slip-rates along an active strand of the Chaman fault are added to the sporadic data set of this poorly investigated transform system. Field investigations coupled with high-resolution GeoEye-1 satellite data of an alluvial fan surface (Bostankaul alluvial fan) show ~1150m left-lateral offset by the fault since the formation of the alluvial fan surface. A weighted mean 10Be exposure age of 34.8±3kyr for the Bostankaul alluvial surface yields a slip-rate of 33.3±3.0mm/yr. This rate agrees with the geologically defined slip-rates along the Chaman fault, but is approximately twice as large as that inferred from the decade-long global positioning system measurements of 18±1mm/yr. The contrast in geomorphic and geodetic slip-rates along the Chaman fault, like other major intra-continental strike–slip faults, has two major implications: 1) the geodetic rates might represent a period of reduced displacement as compared to the averaged Late Pleistocene rate because of transient variations in rates of elastic strain accumulation; or 2) strain partitioning within the plate boundary zone. While strain partitioning could be the reason of slip-rate variations within the western Indian plate boundary zone, transient strain accumulation could explain contrasting slip-rates along the Chaman fault at this stage in its poorly understood seismic cycle.
•Chaman Fault marks oblique convergence at western Indian plate boundary.•10Be dates on displaced landforms along this fault give Late Quaternary slip-rate.•The estimated ~33mm/yr slip-rate is twice as larger than the geodetic slip-rate.•Transient strain accumulation along the Chaman fault.
Reactive powder concrete (RPC) is an advanced cementitious material with ultra-high strength, remarkable durability and excellent toughness. However, temperature dependent creep is a major concern as ...very little work has been reported in the literature. Therefore, systematic investigations are still missing in state of the art. This paper focuses on the impact of Polypropylene (PP) and hybrid (steel and PP) fibers on creep behavior of RPC at elevated temperature. Temperature-dependent creep is further characterized into free thermal strain (FTS), short-term creep (STC) and transient strain (TS), based on different thermo-mechanical regimes. Varying heating and loading schemes were considered such as steady-state and transient thermo-mechanical conditions. The target temperatures considered for steady-state thermal conditions and transient case are 120, 300, 500, 700 and 900 °C. Compressive strength was considered up to 60% load ratio of ambient and temperature dependency. The result shows that STC increases with increasing stress level and higher target temperature. The increase in STC becomes obvious above the transition stage of quartz aggregate. Furthermore, HRPC have significantly higher STC than PRPC and other traditional types of concretes. The evolution of FTS and TS was quite slow below 250 °C. However, at high temperature significant increase in FTS and TS were observed. Furthermore, increasing stress level and the addition of steel fibers results in high TS. Overall, the performance of PP fiber was better than the hybrid fibers on the creep behaviour of RPC. Finally, constitutive relationships were proposed for FTS, STC and TS, which will be used as input data in numerical models of fire resistance calculations.
PDF
