Pseudo-static Test Research Articles

Experimental and numerical studies of a controlled rocking steel frame with buckling-restrained columns

A non-uplifting rocking steel frame with buckling-restrained columns (RSFB) is formed by replacing two side columns in the bottom story of a steel concentrically braced frame with two buckling-restrained columns (BRCs). During major earthquakes, the BRCs first yield to dissipate energy while the other part of the system remains elastic and rotates around the bottom of the middle column to control structural deformation. A pseudo-static test was conducted on the earthquake-resilient RSFB, observing larger out-of-plane deformation occurred in the RSFB first story and the embedment portions of BRCs due to the failure of the out-of-plane restraints. The results indicate that the RSFB needs a stronger out-of-plane restraint to ensure structural performance. A design suggestion for the out-of-plane restraint is subsequently provided. A multi-scale finite element model was established in ABAQUS and validated by the test results, and simulation analyses of the test specimen with full out-of-plane restraints were conducted. The simulation results of this model showed that the hysteresis curve is full under cyclic loads, the lateral drifts are uniformly distributed along the structural height, and the plastic deformation is mainly concentrated in the BRCs energy dissipating portion, implying that the proposed RSFB can yield excellent seismic performance, as expected. Finally, the influences of the BRC embedment lengths on the structural performance and out-of-plane deformation were studied to enhance the out-of-plane stability of the RSFB without full out-of-plane restraints.

Experimental investigation on the seismic performance of low-level corroded and retrofitted reinforced concrete bridge columns with CFRP fabric

Seismic damage mitigation of corroded reinforced concrete (RC) bridge columns in marine environment will be an impending problem in many countries in which a mass of bridges have been constructed for 20 or more years. In this paper, cyclic pseudo-static tests were conducted on three 1/4-scaled RC column specimens with and without retrofit by carbon fiber reinforced polymer (CFRP) fabric in order to investigate seismic performance of low-level corroded columns and the efficiency of CFRP as a retrofit measure. The first specimen was designed with normal design details of Chinese specifications, which worked as a reference. The second and third columns were both corroded with a target of low-level corrosion in the plastic hinge zone using an electrochemical method. Meanwhile, the third column was retrofitted by CFRP jackets in the plastic hinge region. The experimental results were then employed to evaluate the damage process, failure mode, displacement ductility, energy dissipation, lateral resistance strength, and residual displacement of each specimen. The results show that although low level of corrosion in the tested columns, the displacement ductility was significantly reduced due to weakened confinement of the corroded transverse rebars and reduced area of the corroded longitudinal bars. In addition, retrofitting the column using CFRP fabric jackets could significantly increase the displacement ductility and reduce the residual displacement to some extent. It is worth noting that retrofitting of corroded column using CFRP jackets did not improve the lateral strength.

Study on the Scheme of Sensor Arrangement in Pseudo Static Test for Immersed Tunnel Joint

The arrangement scheme of the sensors in a pseudo static test for an immersed tunnel joint was revealed in this paper. To achieve this target, the pushover analysis of the two immersion joint models were studied by using numerical calculation. The mechanical characteristics of the immersed tunnel joint under horizontal loading condition were carefully observed. According to the numerical results, shear keys and connecting part in tunnel elements are the key observation sections, the stress development, the shear capacity and the deformation features of the immersion joint should be measured. Furthermore, a loading system of pseudo static test for immersion joint is also developed. Based on the loading system and numerical funding, the locations for deploying sensors were determined. The scheme of sensor positions played a crucial role in guaranteeing the successful completement of the experiment, and also can offer some reference opinions for similar experiments.

Experimental Study on Seismic Behavior of K-type Eccentrically Braced Steel Frame with Semi-rigid Joints

In order to study how different connection types and floor height affect the seismic behavior of eccentrically braced steel frame, there has been processing 4 pseudo-static tests for eccentrically-braced steel frame, including two one-layer specimen and two three-layer specimen. The seismic behavior of the specimen has been analyzed according to hysteresis curve, carrying capacity, stiffness degeneration, ductility, and energy dissipation ability etc. The experiments’ results show that the connection types have greater impact on seismic behavior, adopting specimen destruction model of high-strength bolts connection as beam segment end-plate weld or web fracture. The rest of components do not appear significant yielding deformation and crack, which caters for post-earthquake restoration and replacement of energy dissipation beam segment. The carrying capacity of high-strength bolts connection specimen is slightly lower than welded connection specimen, but the ductility of the former is far beyond the welded specimen. Because of the slippage between components, hysteresis curves of bolts-connected eccentric braced steel frame structure appear to have pinned phenomenon with various degrees.

EXPERIMENTAL STUDY ON SHEAR BEHAVIORS AND BEARING CAPACITY OF SHEAR WALLS BUILT WITH PRECAST CONCRETE TWO-WAY HOLLOW SLABS WITH VERTICAL JOINTS

Based on the pseudo-static test of five shear walls built precast concrete two-way hollow slabs with vertical joints, the connection behavior of vertical joints is discussed. The effects of key parameters including axial compression ratio, shear span ratio and the number of horizontal reinforcement on the connection behavior of vertical joints and mechanical properties of shear walls have been studied. The result shows that the brittle failure is avoided, the ultimate displacement angle is larger than 1/100, and the displacement ductility ratio was larger than 5.0. During the application stage, the vertical joint is good and the connection between different horizontal assembly units is reliable. When the axial compression increases from 0.15 to 0.25, the shear bearing capacity increases 11.8%, but peak displacement angle decreases 22.5%. As the increase of shear span ratio, the shear bearing capacity decreases significantly. When the number of horizontal reinforcements increases 56%, shear bearing capacity increases 11%. In addition, considering the influence of an interface structure on shear stress, a four-element computational model can be used to calculate the shear bearing capacity as well asthe difference between calculated and experimental values. The difference is less than 6.5%. The model can be used to predict the shear capacity of precast concrete two-way hollow slabs.

Pseudostatic testing for load-carrying capacity of precast concrete-encased steel composite columns

To combine the advantages of concrete-encased steel columns, high-performance concrete and precast structures, an innovative steel composite column encased in precast high-performance concrete is proposed in this paper. The proposed composite column is composed of a precast outer part and a cast in situ inner part. The precast part can be prefabricated using steel-fiber-reinforced reactive powder concrete (RPC), and the inner part can be cast using conventional concrete. With an aim of exploring seismic behavior of this innovative composite column, three of them were designed and subjected to constant axial compression and cyclic loading, with the main test parameter being the shear span-to-depth aspect ratio. The failure mode, hysteresis loop, skeleton curve, lateral stiffness degradation, energy dissipation and displacement ductility ratio were all analyzed to investigate the effect of aspect ratio on cyclic behavior. Test results indicated that no apparent concrete spalling was found in any of the specimens, due to application of steel fibers in RPC, and the structural steel, precast outer-shell and cast in situ inner part behaved compatibly without any visible slippage. Meanwhile, initial stiffness and load-carrying capacity of the test specimens increased with a decrease in aspect ratio, and energy dissipation and displacement ductility increased with the increasing aspect ratio. Based on the test results, two calculation methods (per AISC 360–10 and JGJ 138–2016) were put forward to predict the load-carrying capacity of the test specimens. The model based on AISC 360–10 overestimated the load-carrying capacities of test specimens, while the model based on JGJ 138–2016 predicted capacities that agreed well with the test results.

Seismic Performance of Steel Box Bridge Piers with Earthquake‐Resilient Function

A novel steel box bridge pier with replaceable energy dissipation wall plates at the base was proposed. After moderate earthquakes, the damaged energy dissipation wall plates and constraining steel plates on the two sides could be rapidly replaced, while the entire energy‐dissipated column at the base can also be replaced after rare earthquakes. In this way, the seismic capacity of the new type of steel box bridge pier could be restored after earthquakes. For the purpose of discussing the seismic performance of this novel steel box‐shaped bridge pier, the pseudostatic test and numerical simulation were performed. The results showed that the failure of the specimens in the pseudostatic tests occurred predominantly in the energy dissipation zone at the base. After replacing the damaged energy‐dissipated column at the base, the seismic behavior of the proposed steel bridge pier can be recovered rapidly. Axial compression ratio is an important factor influencing the seismic behavior of the novel steel box bridge pier. The strength of the energy dissipation wall plates influences the novel steel box‐shaped bridge pier’s bearing capacity and deformation capacity. Spacing between the horizontal stiffening ribs had little impact on the bearing capacity and deformation capacity of the proposed steel bridge pier. The larger the thickness of the energy dissipation wall plate, the higher the bearing capacity and deformation capacity of the steel box bridge pier. Finally, an empirical equation for the design of this novel steel bridge pier under cyclic loading was proposed.

Relationship between applied force and magnetic field in a pseudo-static test of a portal frame

Metal magnetic memory (MMM) testing is a nondestructive approach for evaluating the stress concentration and early damage of ferromagnetic components. However, research on the MMM testing of large steel structures has been limited. Thus, this study investigates the suitability of MMM technology for monitoring the damage in steel structures exposed to complex stresses. The normal components of magnetic signals Hp(y) on the beams and columns of a portal frame are obtained through pseudo-static testing. The signal increment ΔHp(y) and its absolute value |ΔHp(y)| under different loads are analyzed. The relationship between the equivalent stress and magnetic signal is investigated through numerical simulation. The results show that the ΔHp(y) curves are similar during the elastic stage but change abruptly during the plastic phase. Moreover, the differences in the magnetic signal directions caused by the varying detection directions cannot be ignored. In the elastic stage, with the increase in the load, |ΔHp(y)| curves initially increase and then decrease. The formation of the ΔHp(y) curve is similar to the distribution of the equivalent stress. The mutation of ΔHp(y) can determine whether a specimen is entering the plastic phase, and can warn against structural failure. The magnetic signal distribution qualitatively reflects the stress distribution.

Restoring Force Model of an Energy‐Dissipation Joint in Hybrid Frames: Simplified Skeleton Curve and Hysteretic Rules

In this paper, a restoring force model, composed of a trilinear skeleton curve and hysteretic rules, is proposed based on nine pseudostatic tests of the energy‐dissipation joint under horizontal low cyclic loading. The critical points of the simplified skeleton curve are obtained via theoretical derivation and FE simulation. The hysteretic rules for the joints are simplified as a concave hexagon, where the parameters of the critical points are optimized by the genetic algorithm (GA). Using the established trilinear skeleton curve, three different working stages, i.e., elastic, hardening, and softening, were divided by the critical points and the moment stiffness of three stages can be calculated. The proposed hysteretic rules of each stage can reveal and explain the “pinching” in the cyclic loading, which make it easier to understand the mechanism of the energy‐dissipation joint. The comparison between the restoring force model and the tests shows that the simplified skeleton curves, the established hysteretic rules, and the ductility and the damping ratio are consistent with the experimental results. Finally, the effectiveness of the established restoring force model is verified.

Seismic performance and design of bridge piers with rocking isolation

Seismic isolation technology has a wide application to protect bridges from earthquake damage, a new designed bridge pier with seismic isolation are provided for railways in seismic regions of China. The pier with rocking isolation is a self-centering system under small and moderate earthquakes, and the unbonded prestressed tendons are used to prevent overturning under strong earthquakes. A numerical model based on pseudo-static testing results is presented to evaluate the seismic performance of isolation bridge piers, and is validated by the shaking table test. It is found that the rocking response and the loss of prestressing for the bridge pier increase with the increase of earthquake intensity. Besides, the intensity and spectral characteristics of input ground motion have great influence on displacement of the top and bottom of the bridge pier, while have less influence on the bending moment of the pier bottom. Experimental and numerical results show that the rocking-isolated piers presented in this study have good seismic performance, and it provides an alternative way for the railway bridge in the regions with high occurrence of earthquakes. Therefore, we provide the detailed procedures for seismic design of the rocking-isolated bridge pier, and a case study of the seismic isolation design with rocking piers is carried out to popularize the seismic isolation methods.

Reinforcement slip model considering corrosion effects

A new bar slip model is developed to account for the contribution of reinforcement anchorage slip to the total displacement of corroded reinforced concrete (RC) members. An analytical procedure is proposed to model the distribution of the reduced bond stress along the corroded steel bar to predict the reinforcement slip in the anchorage area. The reinforcement slip is formulated using an existing model and by new governing equations defined for different bond regions. The possibility of having an insufficient embedment length is also considered, and a corresponding failure criterion is defined. The bar model is validated by comparing the available data from single bar pullout experiments and an existing bar force-slip model. The proposed column model is implemented using a fiber element model to capture both the monotonic and cyclic behavior of corroded columns. Pseudo-static test data from corroded column specimens are used to validate the proposed column model. Overall, the proposed model captures the slip of a single corroded bar reasonably well to accurately simulate the total lateral displacement of columns with corrosion damage.

Pseudo-static test research on EBIMFCW with different shear-span ratio

Purpose The purpose of this paper is to study the seismic performance of the energy-saving block and invisible multi-ribbed frame composite walls (EBIMFCW), changing the shear-span ratio as the test parameter, the low-cycle reciprocating loading tests of six 1/2 scale wall models were carried out. Design/methodology/approach The test design method and analysis are used for the seismic performance of the EBIMFCW. Findings With the increase of shear-span ratio: the walls tend to occur bending failure even more, the initial stiffness of the wall decreases, the overall ductility of the wall is improved and the walls tend to occur bending failure. Originality/value The previous studies do not involve the seismic performance of EBIMFCW under different shear-span ratios. Therefore, the paper studies the hysteresis behavior, ductility, stiffness degradation and energy dissipation performance of EBIMFCW under different shear-span ratios.

Application of spatial lateral constrained loading feedback control method in pseudo-static testing

In seismic performance testing of structures, the accurate boundary condition is the key to guarantee the accuracy of testing results. The one-way pseudo-static testing is the most common loading method in civil engineering seismic testing. However, the structures are all spatial structures in practice, therefore, the lateral constraints on specimen are necessary in one-way pseudo-static testing. The reaction devices are used to constrain the specimen laterally in traditional loading method, but the traditional loading method has some disadvantages such as high cost, large occupation of space and so on. In order to avoid those disadvantages of traditional loading method, a spatial lateral constrained loading feedback control method is proposed in this paper. In this method, the main direction loading and lateral constrain of the specimen are realized by the actuators, and the accurate control of the constraint boundary can be achieved by adjusting the position of the lateral constrained actuators. In order to verify the accuracy and feasibility of the proposed method, a pseudo-static testing of a full-scale two-story three-span single concrete frame is conducted. The experimental results show that the proposed method is reliable, and the experiment accuracy can be guaranteed.

Experimental Research on Seismic Behaviour of Railway Bridge Pier

The shear failure of railway bridge piers has become the main feature of modern bridges. In order to study the shear resistance of railway bridge piers, three models were designed in this paper, including two piers model with a ratio of 1:5 based on Chenglan Railway bridge prototype piers and a test research model. Through the pseudo-static test study on the shear resistance of piers, the failure process of the specimen was given. It was indicated that that A1 and A2 specimen were typical bending failure and possessed enough ductility. And A3 specimen was typical flexure-shear failure. Before loading to yield displacement, stirrup provided little shear strength. After loading to yield displacement, the shear strength provided by stirrup increased gradually with the development of cracks. When the stirrup yielded, its restraint to the core concrete was weaken rapidly, which resulted in the rapid destruction of the bridge pier.

Experimental and numerical investigations on seismic behavior of hybrid braced precast concrete shear walls

This paper experimentally and numerically investigates the seismic behavior of two innovative types of hybrid precast concrete shear walls with diagonal-shaped or cross-shaped concealed bracings. Six 0.75-scaled braced precast concrete shear (BPCS) wall specimens and one monolithic cast-in-situ shear (MCS) wall were fabricated and employed to conduct the displacement-controlled pseudo-static tests. The length and thickness of the specimens were identical, whereas the heights of BPCS wall specimens were different owing to the different shear span ratios (SSRs) of 1.0, 1.5 and 2.0. Using the MCS wall specimen as a reference, the effects of bracing type and SSR on the seismic behavior of BPCS walls were studied in terms of failure mode, hysteretic behavior and energy dissipation capacity. Finite element (FE) analyses of the wall specimens were further performed using the multi-layer shell element model on the Opensees platform. The numerically calculated hysteresis loops of the wall specimens show good agreement with the experimental data, which proves that the employed FE model is adequately accurate in the seismic behavior assessment of BPCS walls. The experimental and numerical results indicate that the developed BPCS walls not only possess similar bearing capacity but also outperform the MCS wall in saving concrete usage and enhancing energy dissipation capacity. The diagonal and cross BPCS walls exhibit diametrically opposite characteristics as SSR increases. The diagonal BPCS wall with low SSR of 1.0 performs better in drift capacity, while the cross BPCS walls are more suitable for earthquake resistance at higher SSRs of 1.5 and 2.0.

In-plane behaviour of composite floor slab diaphragm interfaces under high shear demand

The different failure modes of composite floors subjected to in-plane shear forces have been determined by a number of researchers using pseudo-static testing. However, all previous experimental tests subjected the floors to a combination of shear and moment and did not represent the boundary conditions applying at the diaphragm interfaces with the seismic resisting system. This paper proposes a new experimental test setup in which the slabs being tested are subjected to near pure shear at the slab to supporting beam interface. Using the new experimental test setup, three composite floor slabs have been tested. In the first floor slab, the deck rib orientation is parallel to the supporting beam. For the second and third floor slab configurations, the deck rib orientation is perpendicular to the supporting beam. The second floor slab uses the standard end anchorage details adopted in New Zealand, involving a solid rib of concrete surrounding the shear studs along the secondary beam. The third floor slab uses the standard end anchorage detail adopted in Europe, in which the decking continues over the secondary beam and the shear studs are welded through the decking.It was found that all three slabs had similar strength and stiffness, albeit with different failure modes. The first slab exhibited the most brittle behaviour, whereas the second specimen exhibited a smoother post-peak behaviour and was the most ductile among these three details. A comparison between the test results and existing design equations has been made and a new equation is developed.

Anti-seismic behavior of composite precast utility tunnels based on pseudo-static tests

In this work, we have studied the effects of different soil thicknesses, haunch heights, reinforcement forms and construction technologies on the seismic performance of a composite precast fabricated utility tunnel by pseudo-static tests. Five concrete specimens were designed and fabricated for low-cycle reciprocating load tests. The hysteretic behavior of composite precast fabricated utility tunnel under simulated seismic waves and the strain law of steel bars were analyzed. Test results showed that composite precast fabricated utility tunnel met the requirements of current codes and had good anti-seismic performance. The use of a closed integral arrangement of steel bars inside utility tunnel structure as well as diagonal reinforcement bars at its haunches improved the integrity of the whole structure and increased the bearing capacity of the structure by about 1.5%. Increasing the thickness of covering soil within a certain range was beneficial to the earthquake resistance of the structure, and the energy consumption was increased by 10%. Increasing haunch height within a certain range increased the bearing capacity of the structure by up to about 19% and energy consumption by up to 30%. The specimen with the lowest haunch height showed strong structural deformation with ductility coefficient of 4.93. It was found that the interfaces of haunches, post-casting self-compacting concrete, and prefabricated parts were the weak points of utility tunnel structures. Combining the failure phenomena of test structures with their related codes, we proposed improvement measures for construction technology, which could provide a reference for the construction and design of practical projects.

Research on seismic performance of composite concrete slab with no-protruding rebar shear wall joints

Precast concrete composite slab is one of the most widely used precast elements in civil engineering, which is suitable for all kinds of prefabricated concrete structure. The longitudinal bars at the bottom of precast slab extend beyond the ends of it, which brings a lot of inconveniences in fabrication, transportation and installation. In order to avoid those disadvantages of traditional precast concrete composite slab, a new no-protruding rebar concrete slab shear wall joint is developed in this paper. And five concrete slab-shear wall joint specimens were fabricated to research the joint structure of composite slab with no-protruding rebar but including additional rebar. In order to verify the seismic performance of the new concrete slab-shear wall joint, Pseudo-static testing of those specimens were carried out and the bearing capacity, stiffness, ductility and energy-dissipating capacity of different specimens were compared. The experiment results show that the additional rebar is necessary to the joints of composite slab with no-protruding rebar shear wall to ensure the seismic reliability of the joint connection; the bearing capacity and ultimate deformation of the new no-protruding rebar concrete slab-shear wall joint increase with the increasing of the lapped length of additional rebar.

Experimental investigation of damaged circular reinforced concrete columns with pre-tensioned steel hoops

External confinement can be applied to improve the ductility and energy dissipation capacity of reinforced concrete columns. In this study, the seismic performances of the damaged and undamaged reinforced concrete columns with pre-tensioned steel hoops are investigated. Considering the effects of the damage rate and axial compression ratio, the pseudo-static test was carried on the eight experimental specimens with the reduced scale of 1:1.5. The experimental results show that the ductility and energy dissipation capacity of damaged and undamaged reinforced concrete columns can be effectively improved using the pre-tensioned steel hoops. Moreover, the size effects of columns and the effects of concrete strength are also examined. Finally, based on the experimental results and discussions, several design considerations of pre-tensioned steel hoops for damaged columns are proposed.

Seismic Performance of Reinforced Concrete Short Columns Subjected to Freeze–Thaw Cycles

Previous research shows that freeze–thaw cycles represent one of the most dangerous threats to reinforced concrete (RC) structures. However, there is almost no experimental data on the effects of freeze–thaw cycles on the seismic behavior of RC columns showing flexure-shear failure. In this study, three columns with the shear span-to-depth ratio of 2.5 were subjected to different numbers of freeze–thaw cycles (FTCs) and pseudo-static testing. The seismic performance indexes of the specimens were analyzed in terms of hysteretic behavior, skeleton curves, shear deformation, and energy dissipation. The test observations show that the failure patterns of the test columns altered from the flexure dominated to shear dominated, owing to the more severe deterioration in shear capacity induced by freeze–thaw attack than in flexure capacity. The test results also indicate that freeze–thaw cycles significantly decrease the ductility and energy dissipation of test columns, and they increase the contributions of shear deformation to the total deformation.