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This paper discusses the negative bending behavior of a new type of web-embedded U-shaped steel-concrete composite beams (WUSCBs). Considering the effective width of the concrete slab, a negative bending moment test was performed on eight WUSCB specimens. The web-embedded shear connector in the WUSCB has been shown to have good shear connection performance and maintain the overall function of the WUSCB. The failure process of the specimen was categorized by the cracking, yielding, and buckling loads which correspond to 0.29 Pu, 0.79 Pu, and 0.90 Pu, respectively. Negative bending failure was observed in the WUSCB, evidenced by the steel plate yielding and concrete slab cracking. The WUSCB was found to have good ductility and deformability under negative bending. A finite element model was established to verify with the experimental results. The calculation method for negative bending capacity is proposed; and the calculation results are in good agreement with the test results.

To optimize conventional composite beam, this paper proposes a new steel-concrete composite beam without top flange, and discusses the shear behavior of this novel web-embedded steel-concrete composite beam (WSCB). Five patterns of embedded shear connectors are proposed, including the shapes of swallow tail, gear, modified gear, circular hole, and steel bar. A shear experiment on ten specimens with the shear span ratio λ = 1.5 were conducted, considering effects of the concrete slab width ( B) and the shear connector pattern. The experiments showed two typical shear failure modes depending on the shear connector type. All five kinds of shear connectors guaranteed good integral action in the specimens. The concrete slab width B shows an obvious positive effect on the shear capacity and ductility. Furthermore, a FE model was established and verified by the experimental results to investigate the shear mechanism of WSCB. According to the experimental and numerical analysis results, a specific calculation method for the shear capacity of the WSCB is proposed, which includes the contributions from the steel web and concrete slab.

The seismic behavior of special-shaped concrete-filled steel tubular (CFST) column to H-shaped steel beam plane frame (SCFSTF) with vertical rib connections was investigated experimentally and numerically in this study. Double-bay two-story SCFSTFs with the scale ratio of 1/2 were tested under constant vertical compressive load and cyclic horizontal loads (or displacements), which is a pseudo static experiment considering the axial load ratio. Based on the experimental results, failure modes, bearing capacity, hysteretic curve, skeleton curve, energy dissipation, ductility, rigidity degradation and strength degradation of SCFSTFs were investigated. As a result, a typical strong column-weak beam failure mode was determined. The degradation in strength and rigidity were minimal and energy dissipation capacity and ductility of frames were adequate, demonstrating excellent seismic performance. Besides, energy dissipation capacity and horizontal resistance were improved with axial load ratio increasing within the parametric range of this test. After the test, a finite element method based on software ABAQUS was carried out to further investigate the seismic performance. The numerical results of skeleton curve, rigidity, yield load, peak load and stress distribution agreed well with the test results. The plastic hinge formation process and ultimate failure mode were further investigated using the finite element model.

To investigate the seismic behavior of joint between special-shaped concrete-filled steel tubular (CFST) column and H-section steel beam, a pseudo-static test was carried out on five specimens with scale ratio of 1:2. The investigated factors include stiffening types of steel tube (multi-cell and tensile bar) and connection types (exterior diaphragm and vertical rib). The failure modes, hysteresis curves, skeleton curves, stress distribution, and joint shear deformation of specimens were analyzed to investigate the seismic behaviors of joints. The test results showed the connections of exterior diaphragm and vertical rib have good seismic behavior and can be identified as rigid joint in the frames with bracing system according to Eurocode 3. The joint of special-shaped column with tensile bars have better seismic performance by using through vertical rib connection. Furthermore, a finite element model was established and a parametric analysis with the finite element model was conducted to investigate the influences of following parameters on the joint stiffness: width-to-thickness ratio of column steel tube, beam-to-column linear stiffness ratio, vertical rib dimensions, and axial load ratio of column. Lastly, preliminary design suggestions were proposed.

Three large-scale connections between circular concrete-filled steel tubular columns and H-section steel beams were tested. The specimens include one connection with T-shaped stiffeners under static load and two connections, respectively, with T-shaped stiffeners and diaphragms (including interior and exterior diaphragms) under cyclic loads. During the test, the experimental phenomena were observed. The static properties of strength and ductility are calculated for static connection based on load–displacement curves, while the seismic properties of strength, ductility, and energy dissipation are analyzed for seismic connections based on hysteretic load–displacement curves. Combining experimental phenomena, mechanical properties, and stress development, the beam-hinge failure mode can be identified for all specimens. The measured beam strengths of specimens are compared with those predicted by the current AISC-360, EC4, and GB 50017-2017 codes. The study results show that all connections are reliable. A finite element model, established and verified with the experimental results, is used to perform parametric analysis. Furthermore, design suggestions of T-shaped stiffeners and diaphragms are proposed based on a parametric analysis.

Three large-scale connections between square concrete-filled steel tubular (CFST) columns and H-section steel beams were tested. T-shaped vertical anchorage was used as the embedded elements and bo...

This paper discusses the shear transfer behavior at the interface between circular tubed column and steel beam. Five beam-column connection specimens with crossing diaphragm were tested under monotonic loads, considering the key parameters of joint tube thickness, embedded diaphragm width, and crossing diaphragm thickness. Based on the experimental results, typical failure modes and load-displacement curves were obtained and discussed in details. A simplified finite element model was developed and validated with the experimental results. Parametric studies on the shear transfer capacity were carried out and analyzed. Lastly, practical formulas for estimating the shear transfer capacity are suggested.

This paper discusses a novel configuration of rebar truss stiffened cold-formed U-shaped steel-concrete composite beams (RCUCB). The open steel U-section is stiffened by a rebar truss. The interface between concrete slab and lower part (including steel U-section, encased concrete, and reinforcement) is enhanced with uniformly distributed inverted U-shaped rebars. The reinforcement is installed at the bottom of the lower part to control the concrete longitudinal deformation. A flexural experiment on ten specimens was conducted considering reinforcement ratio, steel ratio, beam depth, and shear stud spacing (at the bottom of steel U-section). Typical flexural failure mode was observed and the rebar truss and inverted U-shaped rebar were found to provide significant integrity for the RCUCB. Thus, the RCUCB can achieve plastic bending capacity and excellent deformability. The mid-span deflection, plastification factor, and ductility factor of the RCUCB are up to L0/20, 2.08, and 24, respectively. An effective slab width of b + L0/3 may be chosen according to the strain distribution. The bending capacity calculated according to EC4 and JGJ 138-2016 agrees generally well with the test result. Finally, design details pertaining to the width to thickness ratio of bottom steel soffit, the height to thickness ratio of steel web, the transverse reinforcement ratio of concrete slab, and bottom longitudinal reinforcement are suggested accordingly.

This paper discussed the stiffness and cracking behavior of a new kind of reinforcement-stiffened cold-formed U-shaped steel and concrete composite beam (RCUCB) under negative bending. The ...

11 integrated multi-cell concrete-filled steel tubular (CFST) stub columns were tested under concentric compression. The key factors of width-to-thickness ratio (D/t) of steel plates in column limb and prism compressive strength of concrete (fck) were considered and their influence on failure mode, bearing capacity, and ductility of the columns were investigated. The experimental results show that: (1) the constraint effect for concrete provided by the multi-cell steel tube cannot be overlooked; (2) the ductility decreases with the increasing ratio D/t of the connecting steel plates for the multi columns; and (3) the bearing capacity increases, while the ductility decreases, with the increasing fck. The finite element (FE) method was used to simulate the integrated multi-cell CFST stub columns and to verify the test results. A parametric analysis using the FE method was carried out to study the effects of the steel ratio α, steel yield strength fy, concrete strength fck, and D/t on the stiffness, bearing capacity, and ductility of the columns. Furthermore, the measured bearing capacity values were compared to those estimated by the Chinese, European, and American design codes. This study shows that the bearing capacity of integrated multi-cell CFST stub column can be reasonably predicted by the design method specified in GB 50936-2014 or EC4-2004 code.

This paper presents a new configuration of rebar truss stiffened cold-formed U-shaped steel-concrete composite beams (RCUCB), of which the upper opening part of the steel U-section is connected by a rebar truss so that the torsional stability can be enhanced. A bending test was carried out on ten specimens considering the following three parameters: shear connection degree, tensile reinforcement ratio, and beam depth. The specimens exhibit three failure modes under certain conditions: longitudinal slip when tensile reinforcement is absent and the full shear connection cannot be attained; vertical uplift when the beam is furnished with detailed longitudinal tensile reinforcement or a full shear connection; both splitting and uplift when the beam is provided with a full shear connection. It is found that RCUCB possesses both high bending capacity and good ductility. Cracks and deformations are mainly controlled by the longitudinal reinforcement, while the ductility is improved by shear studs. The ductility factor can reach 17.6 by optimizing the configuration of longitudinal reinforcement and shear studs and the slip between the steel and the concrete can be reduced by 91% when the beam is installed with detailed longitudinal tensile reinforcement. Moreover, the ultimate bending capacity was calculated according to the EC4 and JGJ 138 codes with the consideration of the following three modification factors: λ b, λ h , and λ c to account for the effective width of the slab, the effective depth of steel web, and the actual concrete compressive strength, respectively. The calculated values agree well with the test results.

A total of 11 L-shaped multi-cell concrete-filled steel tubular stub columns were fabricated and researched in axial compression test. The key factors of width-to-thickness ratio D/ t of steel plates in column limb and prism compressive strength of concrete fckwere investigated to obtain influence on failure mode, bearing capacity, and ductility of the specimens. The test results show that the constraint effect for concrete provided by multi-cell steel tube cannot be ignored. The ductility decreases with the increase of width-to-thickness ratio D/ t of steel plates in column limb. The bearing capacity increases and the ductility decreases with the increase in prism compressive strength of concrete fck. A finite element program to calculate concentric load–displacement curves of L-shaped multi-cell concrete-filled steel tubular stub columns was proposed and verified by the test results. A parametric analysis with the finite element program was carried out to study the influence of the steel ratio α, steel yield strength fy, prism compressive strength of concrete fck, and width-to-thickness ratio D/ t of steel plates in column limb on the stiffness, bearing capacity and ductility. Furthermore, the design method of bearing capacity was determined based on mainstream concrete-filled steel tubular codes.

Six L-shaped and twelve T-shaped concrete-filled steel tubular (CFST) stub columns subjected to axial compression were experimented in this paper. The L-shaped CFST stub columns were welded vertical stiffener at the concave corner. The T-shaped CFST stub columns were stiffened by steel plate stiffeners. During the test, the experimental phenomenon and failure mode of special-shaped CFST stub columns were observed. According to axial load-displacement curves, mechanical properties such as stiffness, bearing capacity and ductility were compared and analyzed. According to the load-strain curves and load-stress curves, strain and stress development of steel tubes and constraint effect for concrete provided by steel tubes were studied. The test results show that the stiffeners can effectively delay the local buckling of steel tubes, increase the buckling capacity, and increase the constraint effect for concrete. The cross-sectional dimension of specimens has no obvious effect on the ductility and the failure modes of T-shaped CFST stub column due to the restriction of steel plate stiffener, while obviously affects the stiffness and the bearing capacity. Finite element (FE) software ABAQUS was used to analyze special-shaped CFST columns subjected to axial compression and the simulated results were in good agreement with the experimental results. Further parameter analysis with ABAQUS was carried out to study the influences of the steel ratio α, steel yield strength fy, concrete strength fck and slenderness ratio λ. Based on the experimental results and FE analysis, design formulae for calculating sectional bearing capacity and stability bearing capacity of special-shaped CFST columns are proposed.

The seismic performance of T-shaped CFST column to H-shaped steel beam joint with vertical rib stiffeners was investigated experimentally and numerically in this study. Specifically, the joint shear deformation, inter-story drift ratio, joint stiffness, and energy dissipation capacity were analyzed. The test results demonstrate that the joint with vertical stiffeners has good seismic behavior and meets the requirements of Eurocode 3 for rigid joints in a braced frame. A finite element model for the multi-cell T-shaped CFST column to H-shaped steel beam joint with vertical rib stiffeners was established to investigate the influences of the following parameters on joint strength and joint stiffness: the width-to-thickness ratio of steel tube, vertical rib dimensions, and the axial load ratio of column. The numerical results indicate that the width-to-thickness ratio of steel tube and vertical rib dimensions play an important role in improving the joint strength and stiffness. A mechanical model for the joint strength was also developed, in which the contributions from the front face and side faces of steel tube and the vertical rib stiffeners were considered. To facilitate the practical design, a simplified design method for joint strength as well as the design suggestions for detailing are proposed based on the mechanical model.

In order to study the fire resistance of T-shaped concrete-filled steel tubular (CFST) columns subjected to eccentric loading, a series of fire tests were conducted along with a numerical study. Specifically, six half-scaled T-shaped CFST columns were tested under the ISO-834 standard fire; and the parameters of stiffener type, load eccentricity, and load angle were considered. The failure modes, thermal response, and structural response were investigated. The test results show that the fire resistance of T-shaped CFST columns decreases with the increase of load eccentricity, but at a lesser degree for relatively high eccentricity. The load angle also has a significant influence on the fire resistance of the columns. A finite element (FE) analysis was then conducted to establish the temperature field model and the thermo-mechanical coupling model which were both validated by the test results. Furthermore, an extensive parametric study including 2008 FE analyses was carried out to investigate the effects of key parameters on the fire resistance of T-shaped CFST columns, including load ratio (n), slenderness ratio (λ), column limb width (B), column limb depth-to-width ratio (D/B), load eccentricity ratio (e/r0), steel ratio (αs), material strength (fy and fck), and load angle (θ). The parametric study indicates that the load ratio n has a significant effect on the fire resistance of T-shaped CFST columns and the other parameters also have certain influences on the fire resistance when n

The connection between special-shaped concrete-filled steel tubular (CFST) column and steel beam is a particular concern to engineers. A novel U-shaped diaphragm connection is introduced in this paper to transfer the moment at beam ends in the frame with special-shaped CFST columns and steel beams. Five T-shaped CFST column to H-section steel beam connections were tested under low-cycle horizontal loading. U-shaped diaphragm was used as the connection to transfer loads from beam to joint panel zone. The experimental parameters include the size of U-shaped diaphragm and the axial load ratio of column. Based on the experimental results, the strength, ductility and strain distribution of the connections were calculated. Test results show that the connection can develop plastic bending capacity in the beam, satisfying the design code requirements of America, Great Britain, and China. Furthermore, a parametric analysis was conducted using the finite element method . The influences of U-shaped diaphragm size, tube thickness, and axial load ratio of column were analyzed. Based on the parametric analysis results, a mechanical model is proposed to calculate the yield strength and ultimate strength of U-shaped diaphragm connections. In conclusion, with a proper design, the T-shaped CFST column to H-section steel beam connection using the U-shaped diaphragm can be effectively used in practical applications.

This paper discussed a new web-embedded steel–concrete composite beam (WTSCB). The WTSCB consists of an inverted T-section steel section and a concrete slab. Five kinds of new shear connectors were designed at the web top and embedded in the concrete slab. In comparison with the conventional composite beam, shear connector welds are not necessary in the WTSCB. Push-out tests were conducted to investigate the shear property of the connectors, in which the load transferring mechanism of shear connector was researched and the calculation method of shear resistance was proposed. Then bending tests, considering effective width of concrete slab and shear connection types, were conducted on ten WTSCB specimens. Bending failure mode and excellent deformability were presented in WTSCB specimens. Moreover, the design methods including shear connection degree, bending capacity and elastic bending stiffness were proposed based on Eurocode 4.

A numerical analysis based on previous experiment has been carried out on T-shaped concrete-filled steel tubular columns subjected to constant axial compressive load and cyclic lateral loads. Tensile bar stiffeners were introduced to be welded on inside surfaces of steel tube to postpone its local buckling and to enhance the confinement of steel tube for concrete. A modified fiber-based method was developed to establish numerical modeling program of specimens’ cyclic behavior, incorporating the effect of stiffeners on postponing steel tube’s local buckling and the confinement for concrete. The reciprocating movement of inflection point along frame column is also considered in the numerical program. A simplified arc-length method was employed as iterative control algorithm of the numerical model. Horizontal load–displacement hysteretic curves of specimens were calculated with the numerical model and verified with test results. A restoring force model based on experimental investigation was proposed as simplified method for engineering practice.

This paper presents experimental investigation and numerical investigation on seismic behavior of special-shaped concrete-filled steel tubular (CFST) column to steel beam joints. Exterior diaphragm and vertical rib are respectively introduced as joint stiffeners. A pseudo static experiment was conducted to investigate load transmission mechanism, failure mode and seismic performance index based on load-deformation curves and strain curves. The seismic behavior of the two kinds of joints were compared and evaluated. The classification of the joints by stiffness is conducted according to Eurocode. Inter-story drift of the specimens was calculated with data from laboratory apparatus and verified with test results. A design formula of joint shear resistance based on internal load transmission was proposed for engineering application. A finite element model of special-shaped CFST to steel beam connections was established as a supplement to analyze load transmission mechanism.

The modified direct stiffness calculation (DSC) method for application to damage detection of RC frames based on the stiffness variation index (SVI) is comprehensively studied. Judging from the fact that few techniques were successfully applied to field problems, the objective herein is to apply the modified DSC method to RC frames, and to ensure that it really works. The vibration data recorded of a 12-story RC model frame under a series of shaking table tests (62 scenarios under four earthquakes of various levels) were adopted. The SVI adopted is based on two key parameters: (1) the modal curvature, which is more sensitive to structural damage than the mode shape frequently used, and (2) the modal moment, which is rather insensitive to ambient noises, as it is calculated from the force equilibrium condition . By comparing the present results with those based on a typical index (MDLAC) and the damage status of the frame in the tests, it is concluded that the modified DSC method, along with the SVI, can be reliably applied to the damage detection of RC frames in practice.

In this study, we evaluated the effect of steam explosion of oil palm frond (OPF) and oil palm empty fruit bunch (EFB) on nutrient composition and ruminal fermentation characteristics in vitro. The results showed that steam explosion decreased NDF (P < 0.01), ADF (P < 0.01), and hemicellulose content (P < 0.01) in OPF and EFB. Steam explosion improved the effective energy value of OPF and EFB. In vitro fermentation results revealed that 72-h gas production capacity of OPF and EFB increased by 12.60and 85.06% (P < 0.01), respectively, after steam explosion. Steam explosion had a tendency to improve the concentration of total volatile fatty acids (TVFA) (P = 0.082). In conclusion, steam explosion of OPF and EFB reduced NDF, ADF, and hemicellulose content and increased gas production and TVFA concentration.

The negative bending behavior of the reinforcement stiffened cold-formed U-shaped steel and concrete composite beams (RCUCBs) is discussed in this paper. The negative bending experiment on 10 specimens were conducted and the damage process and corresponding static behavior in each stage are defined. Two distinct failure modes were found depending on whether the inverted U-shaped reinforcement (IUR) is installed or not: ductile plastic failure mode (when installed) and sudden elastic failure mode (when not installed). The IUR was observed to keep the integral action and improve the bending capacity and ductility of a RCUCB. The closed steel U-section stiffened by the reinforcement truss provides significant confinement to the encased concrete and even maintains its integrity after concrete cracking. The study results show that the plastic hinging of the framed RCUCB under vertical loads spreads to about L0/6 and suggest that the effective slab width in the negative moment zone is Be = L0/3 + b, similar to the positive moment case. Lastly, a negative bending design method was proposed, giving good calculations compared to the test results. The slab reinforcement, steel U-section, encased concrete, and bottom reinforcement contribute 53%, 30%, 11%, and 6% respectively to the negative bending capacity on average.

The seismic behavior of (plane) frames with special-shaped concrete-filled steel tubular (CFST) columns (SCFSTFs), H-shaped steel beams, and exterior diaphragm connections was investigated experimentally and numerically in this study. Double-bay two-story SCFSTFs with a scale ratio of 1/2 were tested under constant vertical compressive load and cyclic horizontal loads (or displacements), which is a pseudo-static experiment considering the axial compression ratio. Based on the experimental results, failure modes, bearing capacity, hysteretic curves, skeleton curves, energy dissipation, ductility, rigidity degradation, and strength degradation of SCFSTFs were investigated. As a result, a typical strong column-weak beam failure mode was observed; degradation in strength and rigidity were minimal, and the energy dissipation capacity and ductility of SCFSTFs were adequate, demonstrating excellent seismic performance. Besides, energy dissipation capacity and horizontal load bearing capacity were improved with increasing axial compression ratios within the parametric range of this test. After testing, a finite element method based on ABAQUS was carried out to further investigate the seismic performance of SCFSTFs. The numerical results of skeleton curves, stiffness, yield load, ultimate load, and stress distribution agreed well with the test results. The plastic hinge formation process and failure mode were also further investigated using the finite element method.

This paper discusses the shear connection of a novel configuration of U-shaped steel and concrete composite beam with a reinforcement strengthening system (RCUCB). In the push-out experiment on 11 specimens, the effects of the following influencing factors were investigated: the diameter of inverted U-shaped reinforcement (IUR), the number of IUR, the width of varus flanges, and the details of reinforcement truss (RTR). Based on the test results, two distinctive failure modes were found: ductile slip for the cases with IUR; and sudden fracture at the slab-web interface (neck) for the cases without IUR. According to the failure mechanisms, a more exact calculation method for the longitudinal shear capacity at the neck between concrete slab and beam web is proposed, which results in good agreement with the test results. On average, the concrete neck, IUR, and RTR contribute respectively 53%, 28%, and 19% of the shear capacity. Lastly, a reliable method for determining the degree of shear connection in RCUCB is proposed and verified using the earlier test results.

Design procedures for L-shaped and T-shaped concrete-filled steel tube (CFST) columns subjected to bending and compression loading scenarios were developed through parametric study using finite element (FE) models verified by existing experimental results. The finite element study on this special-shaped CFST column subjected to pure bending considered parameters of steel-to-concrete ratio α, steel yield strength fy, concrete strength fck, and column limb width-to-thickness ratio B/tw (H/tw). For their behavior under eccentric compression, additional parameters of section stiffening pattern, loading angel θ, eccentricity, and axial compression ratio were included. Parametric analysis results show that steel-to-concrete ratio α, steel yield strength fy and column limb width-to-thickness ratio B/tw (H/tw) have obvious influences on the flexural resistances of the special-shaped CFST columns, while concrete strength fck has a small effect and can be ignored. The column limb width-to-thickness ratio B/tw, steel to concrete ratio α, steel yield strength fy, concrete compressive strength fck, loading angle θ, eccentricity e and section stiffening type have significant effects on the N-M correlation curves, and the convex portion of the N-M curves has a certain symmetry. The column limb width-to-thickness ratio B/tw and axial compression ratio n have significant effects on the shape of Mx-My correlation curves. Based on the FE analysis results, design formulae for calculating sectional flexural resistances were proposed for special-shaped CFST columns. Besides, simplified formulae were provided to conservatively predict the resistances of special-shaped CFST section and column under eccentric compression based on extensive analysis results of FE models.

Torsional effects of a novel rebar stiffened U-shaped steel-concrete composite beam (RCUCB) system are discussed in this paper, based on a series of torsional experiments. The rebar truss is welded on the top varus flanges of the open steel U-section to enhance its stability; The inverted U-shaped rebar is furnished to enhance the integral action between concrete slab and beam web; and the bottom rebar is installed to control the interface slip between concrete and steel. The test results reveal that the torsional failure mode of RCUCB is characterized by the critical inclined concrete cracks and crushed inclined struts of the slab, the cracking torsion ratio (ψcr,b) is 0.04–0.05ψu,b, the cracking torque capacity (Tcr) is 0.31–0.44Tu, and the secant stiffness at the ultimate load is 13–25% of the elastic stiffness. Additionally, some influencing factors are found: the elastic stiffness and cracking torque capacity increase with increasing slab width, slab thickness, and web depth; the ultimate torque capacity may be improved by increasing slab width, slab thickness, slab reinforcement strength, web depth, rebar truss, and inverted U-shaped rebars. Moreover, the concrete slab and beam web share a common torsion ratio provided that the inverted U-shaped rebars are adequate; and the crack width in the slab can be controlled by the torsion resisting ability of slab and the restraint action from the beam web. Lastly, design methods for elastic torsional stiffness, Tcr, and Tu of RCUCBs are proposed.

Using the steam generator of Daya Bay nuclear power plant as prototype, a one-dimensional dynamic mathematical model of nuclear-powered steam generator is built addressing the primary side fluid, the secondary side fluid and the inner and outer walls of the u-tubes based on distributed parameter method and reasonable assumptions. A dynamic simulation program is developed based on MATLAB using Runge–Kutta method and dynamic heat transfer performance simulation of steam generator is conducted under varying power. The calculation results show that the outlet temperature of primary side, the vapor saturation temperature and the mass fraction of secondary side agree with actual operating data of Daya Bay Nuclear Power Plant. Outer wall temperature at interface between parallel flow preheating-section and boiling-section is the highest. It provides a theoretical basis for the analysis of steam generator actual operating condition to build a one-dimensional mathematical model of steam generator based on the distributed parameter method and apply in simulation successfully.

This paper discusses the shear behavior of a novel cold-formed U-shaped steel and concrete composite beam (RCUCB) composed of a rebar (reinforcing bar) truss for stiffening the open steel U-section, inverted U-shaped rebars for enhancing the continuity at the interface between concrete web and flange, and longitudinal bottom reinforcement for controlling the slip between steel U-section and encased concrete. A series of shear experiments on eight specimens were conducted, considering steel ratio (ρs), beam depth (H), and the number of bottom shear studs (nd). Two typical shear failure modes, depending on the shear span ratio (λ), were observed: diagonal compression failure when λ = 1.0; and shear compression failure when λ = 1.5. The respective ductility factors are 2.5–4.0 and 9.0–9.7. This indicates that a transitional shear span ratio (λ0) lies between 1.0 and 1.5. It is also obvious that shear lag effect exists in the concrete slab as the longitudinal strain of the concrete slab is 50–200% larger than the edge strain. Excellent integral action is ensured by the rebar truss and U-shaped rebars, thus enabling the concrete flange, web, and steel U-section to resist shear forces together. The steel ratio (ρs) has an obvious positive effect on the shear stiffness and capacity. The height to thickness ratio of the steel web is suggested to be no larger than 100 to avoid a local buckling before the peak load. A calculation method for the shear capacity of RCUCBs is proposed, which considers the contributions from the steel web, concrete, and dowel action.

Inverted T-shaped precast ribbed panels are used as single-span simply supported bottom plates in concrete composite slabs. The panels have regularly distributed holes in the ribs; therefore they are not only convenient for pipeline layout, but also work well with cast-in-situ concrete layer. An experiment of precast ribbed panels was carried out under out-plane vertical static loading; it was found that the panels were damaged due to concrete shear failure between rib holes near supports. This is different from mid-span bending failure observed in similar experiment by other scholars. The main reason is related to size effect of concrete shear plane. Then, finite element simulation was performed by using commercial software ABAQUS to model the failure mode and bearing capacity of the panel under out-plane vertical static loading, the numerical results are in good agreement with the experimental results. Furthermore, an equilibrium method was proposed to estimate the ultimate bearing capacity for mid-span bending failure and concrete shear failure, respectively. Finally, parametric analysis with the equilibrium method was done to investigate influences of concrete strength and cross sectional dimension on the mechanical behavior of the precast ribbed panels. Compared with the test data and the finite element results, it is concluded that the proposed equilibrium method can predict the failure mode and ultimate bearing capacity of precast ribbed panels.

A three-dimensional computational fluid dynamics model with the thermal phase change model is used to investigate the thermal–hydraulic characteristics of a steam generator with and without quatrefoil tube support plates. The two types of modeled designs are a unit pipe with and one without tube support plates. The computational fluid dynamics simulations capture the boiling phenomena, vortex and recirculation distributions, and the periodic characteristics of the circumferential wall temperature in the regions surrounding the tube support plates. The cross-flow energy responsible for flow-induced vibration damage in the region of the U-bend tubes is obtained with the aid of these localized thermal–hydraulic distributions. A comparison between the key parameters of the unit pipe models with and without tube support plates clearly reveals the influence of tube support plates in guiding flow behavior and alleviating flow-induced vibration damage for a steam generator’s U-bend tube bundle. Therefore, this computational fluid dynamics model can provide technical support for optimizing tube support plate design and improving the thermal–hydraulic characteristics of steam generator.

A three-dimensional “unit pipe” model coupled with broached tube support plates (TSPs) is developed to investigate the influence of TSPs on the thermal-hydraulic characteristics of the primary and secondary side of steam generator (SG). The model reasonably captures the unbalanced boiling phenomena in the SG secondary side, particularly in the regions surrounding the TSPs. At these points, there is an abrupt increase in secondary fluid velocity, generating recirculation distribution and local vortex. Nonuniform outer wall temperatures periodically fluctuate around the circumference of the tubes at the TSPs, with the corresponding temperature difference between the support location and flow hole gradually decaying in the primary flow direction. These thermal-hydraulic distributions are then used to determine the cross-flow energy, which is strongly related to flow-induced vibration (FIV) damage. According to the FIV distributions, FIV damage is predicted to be most severe at angles of θ = 65° on the cold-leg side and θ = 120° on the hot-leg side of the U-bend tube bundles. These simulated FIV damage results are in agreement with the measured plant data from a prototypical SG. Therefore, this developed “unit pipe” model can provide technical support to help alleviate FIV damage and minimize the probability of tube failure.

Square concrete-filled steel tubes (CFSTs) are gaining increasing usage in modern construction practice, offering improved mechanical properties and increased material efficiency compared with the individual steel and core concrete components. However, the cross-section slenderness of the encasing steel is, although more inflexible than a comparable hollow steel tube, restrained due to local buckling. A number of innovative kinds of reinforcement stiffeners have been put forward particularly for the square CFSTs with slender sections of encasing steel. To investigate the mechanical effect of the reinforcement stiffeners and compare them with traditional ones in practice, four square CFSTs welded with various reinforcement stiffeners and one reference CFST have been tested, and are presented in this paper. The mechanical behaviors such as the resistance, ductility and failure modes investigated during the test were also studied in the theoretical research, which was carried out to predict and further summarize the comprehensive properties of the specimens. A numerical analysis program was written and verified with related scholars’ experimental data, and extensive parametric analysis was conducted to investigate the influencing parameters on mechanical properties. Design recommendation for the cross-section strength has been put forward based on the test results and previous research.

Civil engineering educational circles have always been focusing on the professional qualities and cultivation of civil engineering students, which is also problems in civil engineering teaching. In the beginning of professional course teaching, the author introduced an real project accident and specially emphasized that responsibility, teamwork, seriousness, carefulness, comprehensively applying of knowledge, working in accordance with codes are considered as quality requirements of civil engineering students. This teaching thought is carried out through the whole teaching process, which brings deep impression to students and good teaching effect. The teaching thought is introduced in this paper.

Special-shaped column structures improve residential architectural space, compared with traditional frame structures. However, in respect to applicable building height and seismic fortification intensity, traditional special-shaped reinforced concrete (RC) columns have strict limitations in seismic behavior, which hampers further generalization and application of special-shaped columns. Due to increase in constraint effect for concrete, special-shaped concrete-filled steel tube (CFST) columns are expected to behave advantages on the strength, ductility and seismic behavior over special-shaped RC columns. However, special attention should be paid to prevent the steel plates’ premature local buckling and the separation between steel tube and concrete at inner corners. The battlement-shaped bar stiffeners and tensile bar stiffeners, welded on tube surfaces, were first put forward in this paper. Experimental study of 9 stubs in three groups subjected to axial loads was conducted, and the specimens consist of 3 square stubs (including 1 non-stiffened and 2 stiffened CFST specimens) and 6 T-shaped stubs (including 1 RC specimen, 2 non-stiffened and 3 stiffened CFST specimens). Failure modes and static properties of the specimens were investigated. Experimental results reveal that: Due to the constraint effect provided by T-shaped tubes, the CFST specimens behave advantages on the RC specimen in the ascending stiffness, peak resistance and ductility (except for the battlement-shaped bar stiffened CFSTs). For square and T-shaped stiffened CFST specimens, the stiffeners improve their ductility, especially the tensile bar which gives the best performance in ductility and improves the peak resistance substantially. The stiffeners postpone the buckling of tubes, and even upgrade the classification of composite sections, without thickening the tubes.

In this paper, a batch of T-shaped concrete-filled steel tubular (CFST) columns, T-shaped steel tube confined concrete (STCC) columns and T-shaped reinforced concrete (RC) counterparts were tested subjected to concentric compressive load or eccentric compressive load. The battlement-shaped bar and tensile bar were developed as stiffeners to delay local buckling in tube wall. The stiffening mechanism, the failure modes of concrete and steel tubes, the strength and ductility of specimens were investigated in detail during the experimental research. A numerical modeling program was developed and verified against the experimental data. The numerical program, which incorporates the effect of the stiffeners on postponing local buckling of the tube and the confinement of the tube on concrete core, was used to carry out comprehensive parametric analysis of influencing factors on the structural behavior of T-shaped CFST columns.

The Stokes-shifted emission spectra were measured for various photoactive biomolecules in aqueous solution and tissue such as tryptophan, collagen, nicotinamide adenine dinucleotide, and flavin. Information is obtained on the molecular activity in the tissue. This new approach allows for the extraction of some new information not obtained from excitation and/or fluorescence spectroscopy for a single spectral scan.

Eight stiffened square concrete-filled steel tubular (CFST) stub columns with slender sections of encasing steel and two non-stiffened counterparts were tested subjected to axial compressive load. Four types of reinforcement stiffeners and steel tensile strips were introduced to postpone local buckling of steel tubes, in which the tensile strip was first used as stiffener in CFSTs. The stiffening mechanism, failure modes of concrete and steel tubes, strength and ductility of stiffened square CFSTs were also studied during the experimental research. A numerical modeling program was developed and verified against the experimental data. The program incorporates the effect of the stiffeners on postponing local buckling of the tube and the tube confinement on concrete core. Extensive parametric analysis was also conducted to examine the influencing parameters on mechanical properties of stiffened square CFSTs.

Stokes Shift Spectroscopy (S3) offers a novel way to rapidly measure spectral fingerprints of complex molecular mixtures in tissue. The changes of key fluorophores from normal state to the malignant state can be reflected by alteration of Stokes Shift Spectra (S3 spectra). S3 measuremen ts can be used to acquire en ough information of different key fluorophores from one spectrum to speed up spectral acquisition time. In this study, we demonstrate the usefulness of the S3 technique to distinguish the malignant tissue from the normal prostate and breast tissues. The optimal wavelength shift constant ( 'O c ) of S3 spectra measurements for prostate/breast cancer detection were determined to be 40 nm. The underlying physical and biological basis for S3 is discussed. For the first time, our work explicitly discloses how and why S3 is supreme in comparison with other conventional spectroscopic techniques. Keywords: Cancerous human breast tissue, Stokes Shift Spectroscopy (S3), tryptophan, collagen, and NADH 1. INTRODUCTION Optical spectroscopy and imaging provide powerful tools for non-invasive screening and clinical diagnosis of diseased tissue. Fluorescence spectroscopy of intrinsic fluorophores has been studied to differentiate cancerous tissue from normal tissue since its first use in 1984 by Alfano [1]. Fluorescence spectroscopy can detect fluorophores at much lower concentration in tissue in comparison with absorption. Researchers can detect the fingerprints of main fluorophores such as: tryptophan, collagen, reduced nicotinamide adenine dinucleotide (NADH), and flavin adenine dinucleotide (FAD) etc. [2-5]. Human tissue is mainly composed of extracellular matrix of collagen fiber, proteins, fat, water, and epithelial cells. Tissues contain a number of key fingerprint endogenous fluorophore molecules: tryptophan, collagen, elastin, NADH, flavin and porohyrins. Tryptophan is an amino acid required by all forms of life for protein synthesis and other important metabolic functions [6], and is accounted as the major fluorophore contributing to protein in tissue. NADH and FAD can be used to probe changes in cellular metabolism [7]. The prim ary fluorophore in hu man tissue extracellular matrix (ECM) is type I collagen [8]. For invasion and subsequent metastasis, tumor cells degrade the surrounding collagen [8]. Conceivably the biochemical or morphologic changes that cause the spectral variations would appear earlier than the histological aberration [4]. Therefore, fluorescence holds a great promise as clinical tool for diagnosing early stage of carcinomas. To demonstrate the efficacy of the spectro scopic technique to distinguish the maligna nt tissue from the normal, a relative novel technique, namely Stokes Shift Spectroscopy (S3) was specially introduced for prostate and breast cancer detection. The S3 spectra of the key fluorophores in human breast tissue were analyzed using the Nonnegative Least Square (NNLS) method [9]. The linear discriminant analysis (LDA) was used to convert bio-molecular alterations reflected in the native spectra associated with process from the normal to cancer into valuable information. Subsequently, the receiver operating characteristic (ROC) curve was generated to evaluate the performance of the NNLS algorithm combined with LDA for diagnosis of human prostate/breast cancer.

The native fluorescence spectra of human cancerous and normal breast tissues were investigated using the selected excitation wavelength of 340 nm to excite key building block molecules, such as reduced nicotinamide adenine dinucleotide (NADH), collagen, and flavin. The measured emission spectra were analyzed using a non-negative constraint method, namely multivariate curve resolution with alternating least-squares (MCR-ALS). The results indicate that the biochemical changes of tissue can be exposed by native fluorescence spectra analysis. The MCR-ALS-extracted components corresponding to the key fluorophores in breast tissue, such as collagen, NADH, and flavin, show differences of relative contents of fluorophores in cancerous and normal breast tissues. This research demonstrates that the native fluorescence spectroscopy measurements are effective for detecting changes of fluorophores composition in tissues due to the development of cancer. Native fluorescence spectroscopy analyzed by MCR-ALS may have the potential to be a new armamentarium.