Nominal Strength Research Articles

Numerical Performance Analysis of Concrete-Filled Hollow GFRP Beams including Inner Surface Bearing Stresses at the Interface

GFRP sections with filler concrete material form promising structural components for structures; therefore, the structural performance of them has been investigated with increasing popularity. However, the performance of these composites degrades when fully composite action cannot be developed at the interface in where the literature hosts limited knowledge. Different techniques, such as abraded and sand-bonded surface treatments, were investigated experimentally to improve the bond-slip behavior between GFRP and concrete; however, there is a need to define shear mechanism at the interface of the numerical models. In this study, first, the average frictional bearing strengths were extracted for the treated and untreated inner surfaces using experimental results; then, the coulomb friction model was utilized to transfer the shear stresses between two dissimilar materials. Numerical models were verified by the experimental results, and different parametric studies were investigated by varying the amount and shape of GFRP in the cross section, compressive strength of concrete including the non-linear material behavior and interface frictional contact models. The findings showed that the interface strength can improve the flexural capacity of the concrete-filled GFRP beams by about 15.4%. Square GFRP box sections can be suggested for the construction of hybrid beams instead of rectangular sections, whereas the 10% areal ratio in a square cross section reached 103% load capacity improvement. The increased nominal compressive strength of concrete in hybrid beams can increase the hollow GFRP beams’ nominal load capacities and elastic stiffness of the hybrid beams in between; however, the relative gain is reduced due to increased compressive strength of concrete.

Bond Behaviors of Steel Fiber in Mortar Affected by Inclination Angle and Fiber Spacing

Considering the random orientation and distribution of steel fibers in concrete, the synergistic reinforcement of steel fibers on concrete is much complex than the bond of single fiber. It is meaningful to study the bond behavior of steel fiber during many actions. With the inclination angle of steel fiber to pullout direction and the fiber spacing as main factors, this paper carried out fifteen groups of pullout tests for hook-end steel fiber embedded in manufactured sand mortar. The inclination angle ranged from 0 to 60°, and the fiber spacing ranged from 3.5 mm to 21.2 mm. The characteristic pullout load-slip (PL-S) curve of steel fibers are given out after treating the original complete curves of each group test. The values of key points featured the debonding, peak and residual pullout loads and slips are determined from the characteristic PL-S curves. Based on a multi-index synthetical evaluation method, the nominal debonding strength, bond strength, residual bond strength and the debonding work, slipping work, and pullout work, as well as the debonding energy ratio, slipping energy ratio, and pullout energy ratio are analyzed. Results indicate that the bond performance represented by above indexes changes with the inclination angle and spacing of steel fibers. Except for the bond mechanism performing the same as aligned steel fibers by pullout test, the bond is dominated by the resistance of mortar to peeling off near pullout surface and scraping along pullout direction. When the inclination angle is over 15° or 30°, the bond performance is generally decreased, due to the peeling off of mortar on surface of transversal section with a certain depth. When the fiber spacing is over than 5 mm, the bond performance becomes worst due to the scraping out of mortar along with the slip of steel fibers.

Uniaxial Compression Failure and Size Effect of Recycled Aggregate Concrete Based on Meso-Simulation Analysis.

Recycled aggregate concrete (RAC) is a kind of five-phase composite material at the meso-level. It has a more complex interfacial transition zone (ITZ) than ordinary aggregate concrete (NAC), which is an important factor affecting the meso-failure of RAC. In addition, the maximum aggregate size plays an important role in the nonlinear mechanical behavior of concrete, which is closely related to the size effect. In this paper, a 2D random aggregate model of RAC is established based on meso-mechanics. The mechanical properties and failure modes of RAC under uniaxial compression are simulated using a plastic damage constitutive model. Through variable parameter analysis, the effects of the properties and thickness of ITZ on the elastic modulus and peak stress of RAC are studied, and the effect of the maximum aggregate size on the size effect of the compressive strength of RAC is discussed. The results show that the ITZ strength has a positive linear correlation with the peak stress and elastic modulus of RAC, while the ITZ thickness has a negative linear correlation with the peak stress and elastic modulus of RAC. Under the same specimen size (D = 100 mm, 150 mm, 200 mm, 300 mm), with an increase in the maximum aggregate size (dmax =20 mm, 25 mm, 30 mm, 35 mm), the nominal compressive strength of RAC increases by 6–10%, and the size effect is gradually weakened. When the maximum aggregate size reaches 30 mm, a decrease in the size effect tends to slow down compared with the maximum aggregate size of 20 mm. The classical Bažant size effect law is applicable to describe the compressive properties of RAC under different maximum aggregate sizes, and has a certain guiding significance for the prediction of the size effect of RAC in practical engineering.

Uncertainty assessment for the Bayesian updating process of concrete strength properties

Reassessment of infrastructure buildings has become an essential approach to deal with increasing traffic loads on ageing infrastructure buildings and to verify the service-life of those structures. Good estimation of the actual material properties is highly relevant for reliable structural reassessment. Although this holds for all building materials, the importance of good parameter estimation is of special importance for concrete structures, where the strength properties show relatively high variation and where the nominal strength properties tend to be too conservative. Modern design guidelines allow to make use of scientific methods such as Bayesian Updating of material properties to enable a more realistic consideration of the actual material properties in the reassessment of existing structures. However, guidelines for application and experience with those methods are not yet reported much or are rather vague [1]. The presented study focuses on the effect of the Bayesian Updating process for material parameters with special emphasis on the number and sampling location of test specimens as well as on the accuracy and confidence in the obtained posterior distribution, since sampling also includes a certain margin of uncertainty. The investigation on the methodological potential and on the uncertainty margin in the updating process in this contribution uses a batch of 14 test results on the concrete compressive strength obtained from drill cores along with the inherent measurement uncertainties from the testing procedure. After a short review of Bayes’ Theorem, the Markov Chain Monte Carlo Method (MCMC) and the bootstrap methodology, all combinations of subsamples of size 1, 3 and 5 specimens were built and provided to the Bayes’ updating procedure via MCMC to determine the posterior distributions. The series of obtained posterior distributions for a certain subsample was used to determine the uncertainty in the Bayesian Updating process by evaluation of the scatter in the expected value, the standard deviation and the 5 %-quantile of the updated distribution. The simulations show the importance of an adequate sample size and quantify the uncertainties arising from the limited number of observations.

Fatigue strength assessment of TIG-dressed high-strength steel cruciform joints by nominal and local approaches

According to the IIW recommendation, the fatigue strength of welded steel joints is defined as independent of the base material in case of the as-welded condition. However, post-treatment techniques can improve the fatigue performance of welded structures, especially for increased base material strengths. Therefore, this paper investigates the effect of TIG dressing, as common post-weld treatment method, on the fatigue strength of high-strength steel S700 cruciform joints. The statistically evaluated fatigue test results reveal a significant increase of the nominal fatigue strength from FAT 90 for the as-welded up to 182 MPa for the TIG-dressed state. The experiments are further compared to recommended and suggested design curves applying both nominal as well as local stress approaches. Focusing on the TIG-dressed state, the suggested increase in nominal stresses is well validated leading to a conservative assessment. In addition, the proposed slope in the finite life region with a value of m1 = 4 shows a sound fit to the statistically evaluated value of m1 = 4.7 for the test results. The local fatigue strength estimation is performed based on a recent proposal using the theory of critical distances. Therefore, linear elastic numerical analysis of the investigated specimens is performed. Again, the resulting S-N curves agree well to the experiments validating the proposed local design approach.

Mechanical properties of corroded carbon steel based on random pit corrosion in marine environment

The corrosion of carbon steel seriously affects the long-term performance of the marine infrastructure. This study introduces an innovative numerical method for predicting the mechanical property degradation of carbon steel in the marine environment. To determine the degradation pattern of mechanical properties of carbon steel with various degrees of corrosion, 48 Q235 carbon steel specimens were subjected to mechanical properties testing after corrosion; a corrosion model with the stochastic distribution of corrosion pits was established based on the Monte-Carlo principle, and finite element analysis was carried out on the mechanical properties of carbon steel after corrosion. The numerical analytical results agreed well with the testing results, proving the model's validity and predicting the mechanical properties of carbon steel at various exposed times. The results demonstrate that as the amount of time exposed to specimens rises, the yield and tensile strength of the specimens decrease dramatically. Comparing the numerical simulation with the testing, the average error of the nominal tensile strength is 4.2%, and the average error of the nominal yield strength is 6.4%. It was further predicted that the specimens' nominal yield strength and nominal tensile strength decreased by 25.57% and 30.86% when the exposed time was 400 days.

Repeated Impact Response of Normal- and High-Strength Concrete Subjected to Temperatures up to 600 °C

With the aim of investigating the response of concrete to the dual effect of accidental fire high temperatures and possible induced impacts due to falling fragmented or burst parts or objects, an experimental work is conducted in this study to explore the influence of exposure to temperatures of 200, 400 and 600 °C on the responses of concrete specimens subjected to impact loads. Cylindrical specimens are tested using the recommended repeated impact procedure of the ACI 544-2R test. Three concrete mixtures with concrete nominal design strengths of 20, 40 and 80 MPa are introduced to represent different levels of concrete strength. From each concrete mixture, 24 cylinders and 12 cubes are prepared to evaluate the residual impact resistance and compressive strength. Six cylindrical specimens and three cubes from each concrete mixture are heated to each of the three levels of high temperatures, while the other six cylinders and three cubes are tested without heating as reference specimens. The test results show that the behavior of impact resistance is completely different from that of compressive strength after exposure to high temperatures; the cylindrical specimens lose more than 80% of the cracking and failure impact resistance after exposure to 200 °C, while impact resistance almost vanishes after exposure to 400 and 600 °C. Concrete compressive strength is found to be effective on the unheated impact specimens, where the higher-strength cylinders retain significantly higher impact numbers. This effect noticeably decreases after exposure to 200 and 400 °C, and vanishes after exposure to 600 °C.

Effect of confining pressure on shear fracture behavior and surface morphology of granite by the short core in compression test

The study on shear fracture behaviour at elevated confining pressure is very meaningful for a lot of practical activities in underground works. To understand the influence of confining pressure on shear fracture behavior, a series of confined rock fracture tests were performed on the short core in compression (SCC) specimens. Uniform confining pressure was applied on the entire surface of the rock specimen in the tests. The results show that the peak load, shear modulus, nominal shear strength and mode II fracture toughness of SCC specimens increase approximatively linearly with confining pressure. The shear fracture surfaces after confined SCC tests were measured by a three-dimensional (3D) optical scanner. Based on fractal and statistical theories, the effect of confining pressure on the morphological characteristics in shear fracture surfaces has been studied in depth. The results indicate the fracture surface roughness decreases slightly with the increase of confining pressure, which can be attributed to the restraining effect on fracture expansion and the friction effect on the two new shear fracture surfaces under large confining pressure. Generally, standard deviations and means for asperity height and standard deviations of slope angle decline with increasing confining pressure. Frequency distributions of aspect orientation become more evenly with confining pressure. Moreover, the feasibility of applying the Mohr-Coulomb criterion in the SCC approach was assessed. It is found that the cohesion and internal friction angle determined by the SCC method are very closed to the values calculated from uniaxial compression tests, indicating that the SCC method are feasible for estimating shear parameters of rock.

Tensile-Mechanical Degradation-Properties and J-C Constitutive Model of Studs after Strong-Acid Corrosion

This paper presents an investigation on strong-acid relations between corrosion rate and corrosion time in 30 studs, dipped into 36% industrial hydrochloric acid through 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, and 72 h, respectively. These corroded studs are performed tensile tests to study failure mode and stress-strain curves in studs with different corrosion time. Thereafter, a 3-D finite element is established through computer program to validate test results, and then analyze mechanical properties along with failure mode of studs exposed to strong-acid corrosion. The analysis results show that the failure mode gradually changes from ductile-damage state to brittle-damage state. The corrosion rates present a non-linear elevation with an increase of strong-acid-corrosion time. The nominal yield strength, the nominal ultimate strength, and the elongation in the corroded studs exhibit a fast-downward trend when increasing corrosion time. However, the degradation of elastic modulus turn into a slow step and the yield strength ratio in studs tends to be steady. The J-C model (Johnson-Cook Constitutive) with updated coefficients can be applied to reflect the constitutive relations in studs after strong-acid corrosion under quasi-static tension conditions. Further, this model can simulate stress flows within studs after strong-acid corrosion. This research results can provide a guide for long-lifetime construction and safe maintenance in steel structural bridge.

Mechanical properties of CFDST column under eccentric compression after exposed to fire

This paper investigates the experimental behaviour of ten square concrete-filled double skin steel tube (SCFDST) columns subjected to eccentric compression after 60 min of fire time. The test parameters included slenderness ratio, eccentricity and hollow ratio. It was found that the slenderness ratio and eccentricity have significant influence on the residual deformation and bearing capacity. However, when the hollow ratio (χ) was 0.72, slenderness ratio has little effect on the bearing capacity. The accuracy of finite element analysis (FEA) models were verified by the presented test results, and they were in good agreement. A FEA model was established to conduct a parameter analysis of CFDST members, and the working mechanism was analyzed in depth. Based on the parametric analysis, it shows that nominal steel ratio, eccentricity and strength of external steel tube have significant influence on the member’s residual bearing capacity under eccentric compression after fire: The residual bearing capacity decreases with the increase of nominal steel ratio. When the eccentricity increased from 0 to 0.6, the bearing capacity can decrease about 42 % after fire. The hollow ratio and concrete strength have little effect on the bearing capacity after fire. With the increase of fire time from 0 min to 120 min, the proportion in bearing capacity of internal and external steel tube gradually increases 16.8 %. Finally, compared with the relevant codes, the results of the T/CCES 7–2020 code were in good agreement with the FEA results.

Effects of stirrup ratio and shear–span ratio on shear failure of geometrically similar RC columns

Very few studies have been dedicated to the size effect on the shear behaviour of reinforced concrete (RC) columns. In particular, there lacks a design equation that can quantitatively represent the effect of related parameters on the size effect on nominal shear strength for RC columns. This work presents a mesoscale numerical analysis of the mechanical response of geometrically similar RC columns subjected to constant axial load and monotonic lateral load. In the numerical model, the inherent heterogeneous nature of concrete and steel/concrete interaction were considered. The numerical model was validated against test results in the literature, and then adopted to conduct a parametric study of the shear behaviour and size effect of RC columns. The investigated parameters involved the shear–span ratio, stirrup ratio and axial load ratio. The results indicated that the nominal shear strength presents an obvious size effect. This size effect on nominal shear strength was gradually weakened as the stirrup ratio and shear–span ratio increased. Moreover, considering the quantitative influence of stirrup ratio and shear–span ratio on size effect, a modified equation was derived to predict the shear resistance of RC columns. Through comparing with available experimental results, the modified equation was demonstrated to be accurate and reliable.

Seismic investigation of reinforced concrete columns with different transverse reinforcements

In this study, cyclic lateral load tests of eight large diameter circular reinforced concrete column specimens are conducted to investigate the feasibility and effectiveness of both single-cross and double-cross lap-spliced crossties on confining reinforced concrete columns. The tests involve four series of specimens—R, S33, S17, and D33 with the same total confinement force of the circular ties and crossties. The confinement forces of the single-cross and double-cross lap-spliced crossties are respectively calculated by multiplying the cross-sectional area of one and two crossties with the nominal yield strength. Firstly, the results reveal a small, nonsignificant correlation between seismic performance and lateral force direction. Therefore, assigning a direction to single-cross or double-cross lap-spliced crossties is unnecessary. Additionally, circular ties outperformed single-cross and double-cross lap-spliced crossties in terms of the confinement effect when the total confinement force is identical. Thirdly, single-cross crossties demonstrate higher confinement effects than double-cross crossties do, and the calculated reduction in the crossties’ circular tie equivalent confinement force is correlated with the crossties’ configuration pattern and confinement force ratio. Finally, RC circular columns with single-cross and double-cross crossties below 33% of confinement force percentage exhibit acceptable seismic performance, values shown later. These findings merit further research and clarification.

Study on deterioration mechanism of soil in Zhouqiao site under salinization

Alkalinity production is one of the most typical and widespread salinization hazards on the Loess Plateau. Based on the characterization of typical flooding sites and the results of salt monitoring, this study investigates the deterioration mechanism of salinization on Zhouqiao site. The orthogonal test was used to simulate the effects of different concentrations of MgSO4, NaCl and CaCl2 under natural conditions on the quality change, salt analysis out location, surface phenomenon, strength and electrical conductivity of the soil at the Zhouqiao site, and to make a preliminary analysis on the mechanism of saline deterioration of the site soil. The results show that the soil column mass increased significantly under the action of salt, and the rate of salt absorption in the soil column decreased when the critical value was reached, and the critical values were different under the action of different kinds of salts. The rate of salt analysis is also influenced by the salt concentration and the number of cycles, which gradually increases with the increase of salt concentration and the number of cycles. The nominal strength of the soil column with the number of cycles, but occasionally increases. The conductivity increases with the number of cycles, and the magnitude distribution of the conductivity of the soil column under the action of different salts is not exactly the same.

Design of stainless steel lipped channel columns subjected to distortional-global interactive buckling using the direct strength method

Currently, there is no detailed approach for designing cold-formed stainless steel lipped channel columns which fail by an interaction between distortional and global buckling. In this paper, the structural behavior of cold-formed stainless steel lipped channel columns that fail in distortional-global interactive buckling is presented. Finite element (FE) models were developed to simulate the members under axial compression. The results obtained from the finite element analysis (FEA) were compared with the test results in terms of failure modes, strengths and load–deformation curves. After successful verification, a comprehensive numerical investigation was undertaken to provide benchmark data for the assessment the nominal strengths predicted by using the current specifications (based on standards from AISI and AS/NZS) and the design equations proposed by Lecce and Rasmussen. The distortional buckling equation in the AISI code leads to overestimation of predicted resistances, while Lecce and Rasmussen’s formula provides conservative predicted resistances for stainless steel lipped channel columns. The AS/NZS code provides a relatively accurate prediction of the strengths. Finally, a design method for stainless steel lipped channel columns is proposed, which provides considerably more accurate predictions. The proposed Direct strength method (DSM) equation has been proven to accurately predict the ultimate capacities of stainless steel lipped channel columns in compression.

Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests

Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens. The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.

Effect of Metakaolin on Strength Properties of Lateritic Soil Intended for Use as Road Construction Material

An excellent all-weather road is essential in providing reliable transportation services that comprise social and economic development elements. However, in most cases, the road has to be constructed on a soft foundation soil where large deformations usually occur, which causes increases in maintenance costs and leads to interruption of traffic service, especially during the wet season. It is necessary to stabilize or improve the in-situ soils. This study explores the potential of using metakaolin to improve the geotechnical properties of lateritic soil for road construction materials. The soil classifies as A-6(4) and CL according to the American Association of State Highway and Transport Officials and the Unified Soil Classification System. The soil was treated with 5, 17.5 and 30 % concentrations of metakaolin by dry weight and was compacted using three compaction energies: British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were carried out to evaluate the effect of metakaolin on the soil investigated. Results showed a general improvement in the engineering properties of the soil with an increase in metakaolin content, particularly when compacted at the BSH energy level. However, the results did not meet the 1500-3000 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification for road base courses. However, 30 % lateritic soil/metakaolin blended soil compacted using WAS and BSH energy levels suffice for use as sub-base in road construction, having met the 750-1500 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification. The Peak CBR value for the treated soil, compacted using the three energy levels of BSL, WAS, and BSH, occurred at 30 % metakaolin concentration with corresponding soaked CBR values of 17, 23 and 31 %. The Nigerian General Specification recommends a nominal strength criterion of a soaked CBR value of 30 and 80 % to be attained by material to be used as sub-base and base course in road construction. Based on the above criterion, only the 30 % metakaolin treated blend compacted at the BSH energy level met the 30 % requirement for sub-base materials.

Influence of stirrup ratio on size effect of shear strength of concrete beam-column joints reinforced with CFRP bars

<p indent="0mm">The shear failure behavior and the size effect of shear strength of carbon fiber-reinforced plastic (CFRP)-reinforced concrete beam-column joints are investigated in this study. The finite element model for failure analysis of CFRP-reinforced concrete beam-column joints was established using a mesoscale numerical method. The mesoscale failure mode and failure mechanism of geometrically similar CFRP-reinforced concrete beam-column joints were studied, and the influence of CFRP-bar ratio on shear strength and size effect law of joints was discussed. The simulation results show that the nominal shear strength of CFRP-reinforced concrete beam-column joints has an obvious size effect, and the size effect of shear strength can be alleviated by increasing the CFRP-bar ratio. In addition, it is found that the size effect of the nominal shear strength of concrete beam-column joints with CFRP bars is more obvious than that of reinforced concrete (RC) beam-column joints. Based on the size effect law of nominal shear strength for RC beam-column joints, considering the effect of stirrup ratio proposed in the previous work, along with the numerical test results in this study, the size effect law was extended and established for the analysis of nominal shear strength of concrete beam-column joints with CFRP bars.

Design, Engineering and Experimental Testing of Tubular Glass Columns

This research revolves around the design, fabrication and testing of tubular glass columns, with particular focus on their redundancy and fire-safety mechanisms; moreover, addressing aspects such as: the column shape; cleaning and maintenance; end connections; geometric tolerances in the glass and demountability. Two alternative circular hollow (tube) column designs are initially developed and engineered to address these aspects, namely: the MLA (Multi Layered with Air) and the SLW (Single Layered with water). In both concepts the main load-bearing structure consists of two concentric laminated glass tubes. Thus, in order to explore the manufacturing challenges and structural potential of these concepts, the prototyping and experimental work focuses on six 300 mm long samples with 115 mm outer diameter that are laminated and fitted into customized, engineered steel end-connections. Particular attention in terms of manufacturing is paid to the lamination process and associated bubble formation, the possible fracture of the glass by internal resin-curing stresses and the interface between the glass tube and the steel end-connections. All samples are laminated with Ködistruct LG 2-PU component. Three samples are assembled using DURAN® (annealed) glass and the other three are using DURATAN® (heat-strengthened) glass. Subsequently, the six samples are tested in compression until failure to investigate the behaviour of the interlayer material, the post-fracture behaviour of the designs, the differences between annealed and heat-strengthened samples, the capacity of the glass tubes and the performance of the end connections. Initial cracks appeared between 95-160 kN (compression strength of 30-50 MPa) in the DURAN® samples and between 120-160 kN (compression strength of 37-50 MPa) in the DURATAN® samples. These loads are lower than the ones estimated by calculations; in specific, the first cracks occurred at 34-64% of the calculated load. Nevertheless, the samples are found to be robust, with a considerable load-bearing capacity beyond the first cracks, leading to a maximum nominal compression strength capacity of up to 152 MPa for the DURATAN® samples and up to 233 MPa for the DURAN® samples.

Flexural cracking behavior of reinforced UHPC overlay in composite bridge deck with orthotropic steel deck under static and fatigue loads

Ultra-high performance concrete (UHPC) has been used to enhance the fatigue resistance of orthotropic steel decks, but the enhancement effect is compromised by UHPC cracks in negative moment regions. This research investigates the flexural cracking behavior of reinforced UHPC (R-UHPC) overlay in composite bridge deck under static and fatigue loads. The investigated behavior included the load-carrying capacity of composite deck, and the cracking process, pattern and resistance of the R-UHPC overlay. Ten composite specimens were tested, including five slabs for the transverse behavior and five beams for the longitudinal behavior. Static tests investigated the load-carrying capacity, strain distribution and nominal cracking strength. Fatigue tests investigated the cracking process and fatigue resistance of R-UHPC overlay. The fatigue process included an internal force redistribution stage (less than10% of fatigue life) and a stable stage (greater than90% of fatigue life). The fatigue resistance of R-UHPC overlay was evaluated with a modified Goodman diagram.

Experimental investigation of CIP and PC beam-to-CECFST column joints with simple connection details under lateral cyclic loading

Due to the excellent structural performance of Concrete-encased concrete-filled steel tube (CECFST) columns, they have been applied in real practice for several years. In addition, precast technology can be utilised in the construction of CECFST composite structures to further improve productivity. To investigate the behaviour of precast concrete (PC) and cast-in-place (CIP) beam-to-CECFST column joints, a total of 6 joint specimens, including 4 PC and 2 CIP specimens, were thus experimentally studied under lateral cyclic loading. In this paper, the main studied parameters included connection details, construction methods and existence of column axial load. The ultimate strength, failure mode, crack patterns and hysteretic performance of each specimen were analysed in detail. According to the test results, the performance of CIP and PC joint specimens were discussed in the aspect of energy dissipation, ductility and damping coefficients, strength and rigidity degradations. It was found that the PC specimens exhibited comparable cyclic behaviour to the CIP specimens in regards to the maximum strength, hysteretic performance and failure mode. Moreover, based on the measured shear strains, contributions of joint shear resistance from steel tube, inner and outer concrete were quantitatively investigated. Thereafter, the development of shear stress in the outer concrete was compared with the nominal concrete shear strengths from American and European design provisions.