Quasi-static Monotonic Loading Research Articles

Timber-timber composite (TTC) joints made of short-supply chain beech: Push-out tests of inclined screw connectors

This paper presents the results of experimental investigations on six-layered, homogeneous glulam beams made of Italian short supply chain beech (Fagus sylvatica L.). At first, the beams were produced and mechanically characterized for bending, then, they were employed to realize timber-timber composite joints and tested under quasi-static monotonic loading. The test configurations were adopted to reproduce connections used in timber-to-timber composite structures for applications in new constructions. Outcomes in terms of connection stiffness, strength, static ductility and failure modes are presented and discussed. Moreover, the experimental stiffness were used to carry out analytical verification at the serviceability and ultimate limit states to extend the validity of the proposed screw and specimen’s configurations.

Research on bond behavior of CFRP-concrete interface under quasi-static cyclic loading

In order to investigate the bond behavior of CFRP-concrete interface under quasi-static cyclic loading, static and quasi-static interface shear tests were conducted on three different adhesive layer thicknesses and two concrete strength grades. From these results, it can be seen that the load-slip envelope curves of the quasi-static cyclic loading specimen is similar to the quasi-static monotonic loading curves. As the adhesive thickness increases, the interface bearing capacity increases, the maximum strain of CFRP plate increases, and the effective bond length slightly increases. The interface failure mode is related to concrete strength. The failure mode of C30 concrete bonded with CFRP plate is cohesive failure of concrete surface layer, while the failure mode of C50 interface specimen is adhesive failure between CFRP and adhesive layer interface. As the thickness of the adhesive layer and the strength of the concrete increase, the interfacial bond strength and maximum strain of CFRP plate increase. It can be seen that the bond-slip envelope curves of the quasi-static cyclic loading specimen coincide well with the curves of the quasi-static monotonic loading specimen. As the magnitude of the cyclic loading increases, the unloading/reloading stiffness degradation, residual slip at zero load increases, and the dissipated energy increases. The fitting resulted in a degradation model of interfacial stiffness during quasi-static cyclic loading.

Monotonic and cyclic sway behaviour of 2-dimensional frames made of pultruded GFRP I-section profiles

This paper presents an experimental study on the structural response of 2-dimensional full-scale frames comprising pultruded GFRP I-section profiles under lateral quasi-static monotonic and cyclic loading, including four different frame configurations, to assess (i) the influence of using different beam-to-column connection systems (one series included cleats and other included cuff parts); (ii) the benefits of using bracings (one series included a cable bracing system); and (iii) the impact of using infill walls (one series included plasterboard panels). The beam-to-column connections and the bracing system were materialized exclusively with stainless steel parts. The results of the monotonic tests showed that the type of beam-to-column connection has considerable influence on the frames’ response, namely on their lateral stiffness; additionally, the frame with bracings and the frame with infill walls exhibited the highest strength and stiffness, respectively, among all series. In the cyclic tests, all frames presented considerable pinching, limiting the energy dissipation; the results showed that the benefits of the infill walls should not be accounted for in design and that the bracing system used is not adequate for seismic areas, as both the plasterboards and the cable bracing system presented non-recoverable deformations/damage that limited their structural contribution from that point forward. The best performing frame series without bracings or walls was simulated using a simple finite element (FE) model. The profiles were modelled using frame elements and the beam-to-column connections were simulated using link elements with the Pivot hysteresis model, calibrated from previous experiments on the beam-to-column connection system. The FE model was able to predict the lateral response with reasonable accuracy, validating this numerical procedure. Then, the FE models were used to evaluate the effects, on the cyclic performance, of including GFRP bracings and a steel plate damper, leading to an improved hysteric response, especially in what concerns the energy dissipation capacity. Overall, the results show that (i) even with ductile connections, the energy dissipation capacity of simple pultruded frames is limited, (ii) although they present high drift capacity; (iii) simple models can be used for design purposes and (iv) they show that the introduction of material-adapted dissipation systems can improve the seismic performance of pultruded frame structures.

Test on Shear Behavior of Double-Sided Thin Steel Plate Shear Wall Filled with Rigid Polyurethane Foam

A double-sided thin steel plate shear wall filled with rigid polyurethane foam (SWR) is proposed. A quasi-static monotonic loading test and quasi-static cycling loading test on shear behavior and the energy dissipation capacity of the SWR were carried out. Four kinds of test specimens, including the pure steel frames, the steel frame with double-sided thin steel plates, the SWR, and the SWR with an open hole, were tested. The results showed that compared with the pure steel frame, the erection of thin steel plates on both sides enhances the shear bearing capacity, initial shear stiffness, and energy consumption capacity. It turns out that the rigid foam polyurethane (RPUF) significantly increases the shear performance of the thin steel plate shear wall. The main reason for this is that the bond effect and support effect of the RPUF delay the out-of-plane buckling of thin steel plates and improve shear performance and energy dissipation capacity.

Numerical simulation of laterite confined masonry building subjected to quasi-static monotonic lateral loading

ABSTRACT The paper attempts to establish a relationship between strength of laterite units and mortar to predict masonry strength and elastic modulus of laterite masonry based on material properties reported in literature. The properties obtained from derived analytical models were used as input parameters for finite element analysis (FEA) of laterite confined masonry (LCM) buildings under quasi-static loading. Numerical studies were performed on LCM buildings up to four stories to study seismic behaviour. LCM buildings upto three storeys demonstrated stresses within the permissible limits for the wall thickness of 150 mm, while four storey LCM building showed high stress concentration exceeding the permissible limits, for which ground storey wall thickness may be increased to 300 mm. One storey LCM building resisted lateral load equivalent to 1.02 g of its mass, while the corresponding values for two, three and four storey LCM buildings were 0.40 g, 0.23 g and 0.13 g, respectively. LCM buildings up to three storey demonstrated maximum damage index in the range of 0.8 to 0.85, indicating collapse prevention state. Howbeit, four storey LCM building exhibited damage index of 0.91 at maximum displacement, which corresponds to collapse state.

Experimental characterisation of as-built and retrofitted timber-masonry connections under monotonic, cyclic and dynamic loading

In the province of Groningen (NL), where human-induced earthquakes take place due to gas extraction, a large part of the building stock is composed of brick masonry walls and timber diaphragms. In this framework, timber-masonry connections play a crucial role in the global seismic response of the buildings, but their properties and structural behaviour have not been investigated yet for the Dutch context. This work describes the experimental campaign conducted at Delft University of Technology to characterize as-built and strengthened timber-masonry connections. The joints were tested under either quasi-static monotonic, cyclic or dynamic loading, to analyse the effect of an induced earthquake signal on the connections’ response in terms of strength, stiffness and damage evolution. The obtained test results provided more insight into the capacity and properties of existing connections, and useful knowledge on the effectiveness of the tested retrofitting methods.

Strain dependent magneto-mechanical property of magnetorheological gel composite: Rheological measurement and model establishment

Controlled over an external magnetic field, rheological response of magnetorheological gel (MRG), a smart composite that could change according to a specific stimulation, could be reversible and adjustable. This paper sheds light on the large deformation-dependent magneto-mechanical property of MRG under different working mode, i.e. quasi-static and dynamic mode, which has rarely been systematically analyzed and compared. The viscoelastic and hysteretic properties of MRG were evaluated by three kinds of experiments that were conducted under different strain excitations—linearly monotonic and cyclic strain, and harmonically cyclic strain. The results reveal that shear stress and normal stress display opposite trend with the increase of strain under quasi-static monotonic loading. A simple parametric model is proposed to describe the shear stress of MRG under quasi-static loading. Furthermore, for quantitatively characterizing the Payne effect of MRG under dynamic loading, the classical Maier-Goritz model predicting the Payne effect of material was modified by introducing a magnetic dipole theory that considers the effect of magnetic field on Payne effect. The magnetic dipole theory is established based on triangular double-chain rather than the conventional single chain. Moreover, in the presence of a magnetic field, the hysteretic loop of MRG would occur a overshoot phenomenon under dynamic working mode, which could not been found under quasi-static cyclic mode. Also, dynamic loading, compared with quasi-static one, could enable MRG to dissipate more energy. This paper is possibly conducive to understanding the working mechanisms about microstructures of MRG and designing MRG-based vibration control devices.

Design and Experimental Analysis of Connections for a Panelized Wood Frame Roof System

This paper presents the results of an experimental study on the short-term mechanical performance of timber screw connections comprising two types of fasteners suitable for a novel panelized roof design process. Thirty-seven specimens of five different connection configurations were tested under quasi-static monotonic loading. The main objective of this study is to provide a preliminary assessment of connection capacity that is key to the successful implementation of a proposed panelized roof design method. It also provides the basis to assist in the development of a numerical model of the novel roof assembly. Additionally, the experimental data are used to check the validity of existing analytical approaches for predicting the strengths of screwed connections comprising engineered wood members. The validation exercise shows that available analytical models can be used to predict the connection capacity of the novel panelized roof.

Anisotropic cyclic deformation behavior of an extruded Mg-3Y alloy sheet with rare earth texture

Mg-RE (magnesium-rare earth) alloys exhibit pronounced in-plane anisotropy of mechanical response under quasi-static monotonic loading resulting from the RE texture, as extensively reported. In this work, an obvious in-plane anisotropy of cyclic deformation behavior was observed in an extruded Mg-3Y alloy sheet during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature. The extrusion direction (ED) samples displayed better fatigue resistance with almost symmetrical hysteresis loops and longer fatigue life compared with the transverse direction (TD) samples. The influences of texture on the deformation modes, cracking modes, and mechanical behavior of Mg-Y alloy sheets under cyclic loading were studied quantitatively and statistically. The activation of various slip/twinning-detwinning systems was measured at desired fatigue stages via EBSD observations together with in-grain misorientation axes (IGMA) analysis. The results indicate that the activation of deformation modes in the TD sample was featured by the cyclic transition, i.e., prismatic slip (at the tensile interval) →{10–12}tension twinning (at the compressive reversal) → detwinning + prismatic slip (at the re-tensile reversal). In the case of the ED sample, the cyclic deformation was dominated by the basal slip throughout the fatigue life. For cracking modes, intergranular cracking and persistent slip bands (PSB) cracking were the primary cracking modes in the ED sample while the TD sample showed a high tendency of {10–12} tension twinning cracking (TTW cracking). The underlying mechanisms influencing the activation of various slip/twinning-detwinning systems, as well as cracking modes and cyclic mechanical behavior, were discussed.

The deformation modes and transferability during low-cycle fatigue of Mg and Mg–3Y alloy

Mg–Y alloys show distinctly different slip/twinning activity under quasi-static monotonic loading at room temperature compared with pure Mg, as extensively reported. In this work, the influences of 3% Y addition on the deformation modes and transferability during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature of Mg sheets were studied quantitatively and statistically. The activity of various slip systems and twinning-detwinning were measured at desired fatigue stages via quasi-in-situ EBSD observations together with slip trace analysis. The results indicate that the activation of deformation modes in pure Mg was featured by the cyclic transition, i.e., tension twinning (at the compressive reversal) → detwinning + basal slip (at the tensile reversal). In Mg–3Y alloy, basal slip dominated the cyclic deformation throughout the fatigue life span. Compared with pure Mg, Mg–3Y alloy displayed the enhanced activity of various slip systems, including basal, prismatic, and pyramidal slip systems, but lower twinning-detwinning activity. For deformation transferability, mk, which is the product of the Schmid factor (SF) and the geometric compatibility factor (m’) values of the adjacent grains, was used to evaluate the slip transferability and twinning transferability at grain boundaries. Mg–3Y alloy showed a higher likelihood of slip transfer but lower twinning transferability than pure Mg. The underlying mechanisms affecting the activity of various slip systems and twinning, as well as deformation transferability and mechanical behavior, were discussed.

Seismic Behavior of Balloon Frame CLT Shear Walls with Different Ledgers

This paper presents experimental investigations on the seismic behavior of cross laminated timber (CLT) shear walls in a balloon frame configuration with various ledger assemblies attached at midheight. The tested system consisted of two seven-ply 191-mm-thick CLT panels with generic hold-downs, steel angle brackets, plywood surface splines, and nails as fasteners. A 2-story system was tested with a panel aspect ratio of 3∶1 with different steel and wood ledgers under monotonic and quasistatic reversed cyclic loading. Three ledgers were subsequently tested under vertical quasistatic monotonic loading to determine their remaining load-carrying capacity. The tests showed that the shear wall displacement was due to the rocking of the wall panels, which themselves behaved as rigid bodies with negligible in-plane deformations. When compared to the monotonic tests, the strength in reversed cyclic tests was up to 21% lower. The ledger did not impede the desired rocking behavior of the wall, nor did the rocking of the wall reduce the remaining gravity load-carrying capacity of the ledgers by more than 7%. Balloon-framed CLT shear walls can be detailed and designed using the Canadian standard specifications for platform-type construction.

Investigation of flexural behaviour of structural timber beams strengthened with NSM basalt and glass FRP bars

Near Surface Mounted (NSM) fibre reinforced polymer (FRP) bars is an effective technique of improving the performance of timber beams. Despite the potential of NSM technique, literature remains limited, whilst there is not any standard method for the prediction of the NSM FRP timber flexural capacity. Extending the pool of experimental data and thus the understanding of FRP strengthened timber structures, the present paper reports an experimental study of timber beams reinforced with glass and basalt FRP bars. Moreover, the paper presents a general theoretical model in order to estimate the moment resistance of the NSM FRP timber beams. The experimental study examined white spruce timber specimens in two reinforcement configurations; one with reinforcement bars only on the tension zone and one with reinforcement bars both on the tension and the compression zone. Control specimens were also included for comparison purposes. All beams had a rectangular cross-section of 70 × 215 mm and were loaded under four-point bending configuration with a 2.3 m span. A total of 20 specimens were tested under displacement control quasi-static monotonic loading. The main failure mechanism observed for both NSM FRP reinforced and unreinforced specimens was brittle tensile failure of the timber at the tensile zone. The load–deflection curves, the strain distribution profiles and the failure modes were discussed. It was observed that a significant increase on the ultimate load (33–69%) and the flexural stiffness (22–33%) of the timber beams can be achieved due to the NSM reinforcement. The proposed theoretical model for the ultimate strength of NSM FRP strengthened timber beams is assessed on the basis of the test results and collated data, showing a good comparison between the experimental and theoretical results.

Martensite Transformation and Superelasticity at High Temperature of (TiHfZr)74(NbTa)26 High-Entropy Shape Memory Alloy

In this work, a (TiHfZr)(NbTa)26 (%at) high-entropy quinary alloy has been developed especially for high-temperature superelastic applications and studied over a large range of temperatures. The mechanical properties of this new material were compared with those of other superelastic alloys. The different ingots have been made in a cold crucible from pure metals. Several thermomechanical treatments have been performed on the microstructure of four alloys among them (TiHfZr)(NbTa)26 alloy. The microstructure of each alloy has been characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and x-ray diffraction technique (XRD) and the mechanical behavior was investigated through three-point bending tests between − 40 and 200 °C, in quasi-static monotonic and low cycle loading conditions. The effects of the thermomechanical treatments on the static and cyclic thermomechanical mechanical responses have been analyzed in combination with the microstructure investigations of the four studied alloys. It has been shown that the (TiHfZr)(NbTa)26 alloy presents a martensitic transformation and a superelastic effect over the studied range of temperatures, in the cold-worked state or after solution treatment. Finally, the obtained experimental results have been compared with those of other superelastic alloys demonstrating the features of the developed high-entropy high-temperature superelastic alloy.

Hyperelastic hold-down solution for CLT shear walls

The use of cross-laminated timber (CLT) shear walls in tall buildings poses large demands on hold-downs (HD). While commonly used HDs behave as dissipative connections, the current Canadian Standard for Engineering Design in Wood recommends designing HDs as a non-dissipative connection. To satisfy this requirement, a hyperelastic elastomeric (rubber) HD was developed. Material level tests showed that the compressive behaviour of rubber layers relied on a dimensionless geometrical shape factor (SF). Component level tests on a total of 16 different HD configurations varying the width and thickness of the rubber pads were conducted under quasi-static monotonic and cyclic loading, the latter with two different loading protocols. Under monotonic loading, the rubber HDs behaved hyperelastic without any residual inelastic deformation and no damage was observed in the CLT panels or the steel parts. The HD load-displacement behaviour was mostly influenced by SF, with smaller SF leading to lower stiffness. A power function was developed to describe the load-displacement behaviour of the HD. Under cyclic loading, no strength or stiffness degradation was observed, even after multiple loading cycles. When designing CLT shear walls with the proposed hyperelastic HD, both the CLT panel as well as the steel parts must be capacity protected to prevent the brittle failure of the CLT or premature yielding of the steel.

Power-Actuated Fasteners Connecting Cold-Formed Sheet Steels under Monotonic Tension Loading

AbstractA total of 105 cross-tension tests were conducted to investigate the strength and behavior of power-actuated fastener (PAF) connections under quasi-static monotonic tensile loading. Three t...

On the low-cycle fatigue response of CoCrNiFeMn high entropy alloy with ultra-fine grain structure

High Entropy Alloys (HEAs) are a new class of multi-component alloys with excellent tensile strength-ductility combination. Their yield strength levels, however, are still low as compared to other high strength materials. Here, Equal Channel Angular Pressing (ECAP) was employed to improve the yield strength of the most well-known HEA, CoCrFeMnNi, through microstructural refinement. The cyclic response of both coarse and ultrafine grained CoCrFeMnNi was investigated during strain-controlled low cycle fatigue tests under fully reversed push-pull loading at room temperature. The microstructural evolution during cyclic loading was compared to the microstructure under quasi-static monotonic loading. Very high yield strength levels around 1 GPa were obtained after ECAP. In addition, ECAP samples demonstrated a superior fatigue life at relatively low strain amplitudes while coarse grained samples exhibited a better fatigue life at the highest strain amplitude considered. X-ray diffraction, electron backscattered diffraction and transmission electron microscopy were performed to reveal underlying mechanisms for the superior fatigue life and the overall transient behavior upon cycling. The fatigue life and hardening behavior were governed by the refined grain size, high density dislocation walls, and the annihilation of existing dislocations resulting in the formation of cell structures in the ECAP samples. The lower fatigue life of the ECAP samples at the highest strain amplitude is attributed to the higher stress amplitudes and cyclic softening due to accelerated dislocation annihilation. Finally, the formation of dislocation cell structures and high-density dislocation walls simultaneously is rationalized by the effect of applied stress on the partial dislocation separation.

Experimental investigation of OSB sheathed timber frame shear walls with strong anchorage subjected to cyclic lateral loading

Sheathed timber frame shear walls (STFSW) with strong anchorage have recently been studied to be used as the main lateral force resisting system in timber buildings. The first part of this research project highlighted the enhancement of the shear stiffness and strength of the STFSWs with strong anchorage in comparison with the established configuration of light-frame timber shear walls under monotonic horizontal loading. In this paper, the in-plane seismic behavior of STFSWs with strong anchorage was further investigated by means of quasi-static monotonic and cyclic loading tests on large-scale timber shear walls. The boundary conditions of the specimens were considered more realistically by applying a combination of vertical force and bending moment on top of the walls. In addition to the ISO 21581, the walls were tested under a new horizontal cyclic loading protocol especially developed for the low-to-medium seismicity regions. The STFSWs with strong anchorage showed a marginally higher shear resistance under cyclic loading. Nevertheless, in terms of ultimate displacement, they did not evidently perform as well as under monotonic loading when subjected to cyclic loading. Withdrawing of staples was the main failure of the stapled connections resulting in the out-of-plane displacement of the sheathing panels, which was clearly observed by the 3D digital image correlation measurement system. The low-to- moderate seismicity loading protocol was not highly influential on their shear resistance and displacement capacity.

Experimental study of variation of models and layers in bamboo’s perpendicular connection to fiber with fiber-reinforced polymer (FRP)

Bamboo is a natural material that is a great demand in the field of simple construction, so connection is one of the things that need to be considered. Research on bamboo connection has been carried out using bolts, steel gussets with wood or mortar fillers, and Fiber Reinforced Polymer (FRP). The use of FRP has advantage since FRP is light, strong, and has adequately high stiffness. This research uses two types of perpendicular connection to fiber (TLS) with two layers methods, different number of layers, and two bolts which function as lateral connection. The used connection testing method is quasi-static monotonic loading. From the results of the study it is found that TLS01-2L increased the maximum load by 80,05 percent compared to TLS01-1L, while in TLS02-2L there is a decrease of 20,65 percent compared to TLS02-1L. In addition, the average ductility value is 2,63 for TLS01 and 2,11 for TLS02 so the stiffness value only reaches 1,75 for TLS01 and 1,97 for TLS02. It can be concluded that the numbers of layer do not affect the strength of the TLS connection but rather the FRP bonding area and the windings method which influences the strength and stiffness of the connection.

Quasi-static tests on a two-story CLT building

A two-story full-scale CLT platform-type building of 4.5 m × 9.1 m in plan, with a height of 5.04 m, was tested under quasi-static monotonic and cyclic loading. The main objectives were to evaluate the global response of the structure, the performance of the shear walls, the behaviour of the connectors (hold-downs and angle brackets) and the frequency response of the structure during the tests. Lateral loads were applied on the storeys inducing torsion to the building. Loading procedure, number and disposition of connectors varied between tests. However, it is important to note that, in order to avoid a possible overlap of effects, the metal connectors hold-downs and angle-brackets only have been placed in CLT shear walls in each loading direction. In terms of performance, longitudinal direction presented a stiffer behaviour when compared to the transverse, where it was possible to verify greater sliding in the longitudinal direction and global rocking in the transverse direction. The results of this experimental campaign will be used for further analytical and numerical analyses, in order to help to implement more detailed seismic analysis, namely pushover, of CLT constructions.

Experimental and numerical analysis of GFRP frame structures. Part 2: Monotonic and cyclic sway behaviour of plane frames

Part 1 [1] of this two-part paper presented an experimental study of the cyclic behaviour of a novel beam-to-column sleeve connection system for pultruded glass fibre reinforced polymer (GFRP) tubular profiles, and the numerical simulation of such behaviour. This Part 2 presents an experimental and numerical study on the sway behaviour of full-scale GFRP plane frames comprising the same tubular profiles and the aforementioned connection system. The GFRP frames were tested under quasi-static monotonic and cyclic loading, with and without infill walls, materialized by composite sandwich panels. The results of the tests show that high-load carrying capacity infill walls have a remarkable effect on the frames’ structural behaviour, significantly increasing their stiffness and load carrying capacity, as well as their cyclic performance, namely regarding energy dissipation. On the other hand, such improvement involved extensive damage in the frame elements, particularly in the beams, which at some point compromised their structural integrity. The numerical study included the simulation of the cyclic tests of the unfilled walls, by means of relatively simple finite element (FE) models, comprising frame elements and spring joints simulating the behaviour of the connections, in which the Pivot hysteresis model calibrated in Part 1 [1] was used. The comparison between experimental and numerical results shows that these simple and design-oriented FE models can provide an effective (and conservative) tool for the simulation of pultruded GFRP frames under horizontal cyclic loads.