Damage detection and system identification with output-only information is an important but challenging task for ensuring the safety and functionality of civil structures during their service life. In this paper, a relatively simple and efficient iteration identification method consisting of the least squares estimation (LSE) technique and an input modification process is proposed for the simultaneous identification of structural parameters and the unknown ground motion. The spatial distribution characteristics of ground acceleration on earthquake-excited building structures are considered as additional information for parameters identification in each iterative step. First, the unknown input is estimated using the measured responses and the initial guesses of the structural parameters. The estimated input is then modified on the basis of the property of its spatial distribution. This modified input is further employed for providing the updated estimation of structural parameters. The iterative procedure would continue until the preset convergence criterion is satisfied. The accuracy of the proposed approach is numerically validated via a shear building model under the El Centro earthquake. The effects of signal noise, the number of sample points, and the initial guesses of structural parameters are discussed. The results show that the proposed approach can satisfactorily identify the structural parameters and unknown earthquakes.

The effects of recycled powder (RP) on hydration, micro-structures, compressive strength and tensile properties of high-ductility cementitious composites (HDCC) were studied. Three mass ratios of RP ranging from 10, 30 to 60% were employed to partially replace the cement. The hydration kinetics of RP-amended matrix was measured to investigate the influence of RP on the cementitious hydration process and the phase development was quantified by the thermal gravimetric analysis. Mechanical properties, including the compressive and tensile properties of HDCCs were obtained at 28 days. The morphology of reinforced polyethylene fiber at the fracture surface was obtained by the environmental scanning electron microscope (SEM) analysis.

To investigate the bearing capacity of the hollow Glass Fiber Reinforced Polymer (GFRP) pipe-concrete-steel tube composite long columns subjected to eccentrical compression load, 33 hollow GFRP pipe-concrete-steel tube composite long columns have been designed. The slenderness ratio (λ), compressive strength of concrete cube (f_cu), eccentricity (e) and so on are the main parameters. Based on constitutive models for steel, GFRP and confined concrete, numerical simulation of the hollow GFRP pipe-concrete-high strength steel tube composite long columns has been carried out by using software ABAQUS. The rationality of the constitutive models and modeling method has been verified by comparing the experimental and simulated load-displacement curves. The influence of different parameters on the mechanical behavior of this kind of column has been investigated. Results show that with the increasing of t1, t2 and fcu, the ultimate eccentrical compression bearing capacity of the specimen increases. With the increasing of e, the ultimate displacement of the specimens increases, while the ultimate eccentrical compression bearing capacity decreases. The eccentricity has a significant influence on the ultimate eccentrical compression bearing capacity. With the increasing of λ, the ultimate eccentrical compression bearing capacity of the specimens gradually decreases. The specimens suffer from ductile failure. The formula of the ultimate eccentrical compression bearing capacity of the composite columns is obtained by statistical regression. The study can provide theoretical support for the application of the composite columns in practical engineering.

The behavior of H‐shaped honeycombed stub columns with rectangular concrete‐filled steel tube flanges (STHCCs) subjected to axial load was investigated experimentally. A total of 16 specimens were studied, and the main parameters varied in the tests included the confinement effect coefficient of the steel tube (ξ), the concrete cubic compressive strength (f_cu), the steel web thickness (t₂), and the slenderness ratio of specimens (λ_s). Failure modes, load‐displacement curves, load‐strain curves of the steel tube flanges and webs, and force mechanisms were obtained by means of axial compression tests. The parameter influences on the axial compression bearing capacity and ductility were then analyzed. The results showed that rudder slip diagonal lines occur on the steel tube outer surface and the concrete‐filled steel tube flanges of all specimens exhibit shear failure. Specimen load‐displacement curves can be broadly divided into elastic deformation, elastic‐plastic deformation, and load descending and residual deformation stages. The specimen axial compression bearing capacity and ductility increase with increasing ξ, and the axial compression bearing capacity increases gradually with increasing f_cu, whereas the ductility decreases. The ductility significantly improves with increasing t₂, whereas the axial compression bearing capacity increases slightly. The axial compression bearing capacity decreases gradually with increasing λ_s, whereas the ductility increases. An analytical expression for the STHCC short column axial compression bearing capacity is established by introducing a correction function (w), which has good agreement with experimental results. Finally, several design guidelines are suggested, which can provide a foundation for the popularization and application of this kind of novel composite column in practical engineering projects.

This study aims to investigate the hysteretic behavior of H‐shaped honeycombed steel web composite columns with rectangular concrete‐filled steel tube flanges (STHCCs). Taking the shear span ratio (λ_s), axial compression ratio (n), steel ratio of section (α), aspect ratio of section (D/B), yield strength of steel tube (f_yfk), and compressive strength of concrete (f_ck) as the main parameters, we designed 22 full‐scale STHCCs. By comparing the load‐displacement curves between test and simulation, the rationality of finite element modeling method was verified. The quasi‐static analysis of 22 specimens was carried out, and the influence regularity of different variables on the hysteretic behavior, skeleton curves, ductility, energy dissipation, resistance degradation, and stiffness degradation of STHCCs was obtained. The results show that the hysteresis curves of all the specimens show full shuttle shape and strong energy dissipation capacity. λ_s, α, and f_yfk have great influence on the bearing capacity of skeleton curves. With the increase of α and f_yfk, the initial stiffness of the specimens gradually increases. The stiffness degradation rate of the specimens gradually slows down, and the energy dissipation coefficient gradually decreases by increasing λ_s, α, and f_yfk, but energy dissipation capacity is still at a high level. The resistance degradation of specimens increases gradually by increasing λ_s, α, f_yfk, and D/B. The ductility of specimens gradually increases by increasing n, α, and f_ck. The maximum bulging deformation and maximum stress of specimens appear at the column foot. The trilinear skeleton curve model and restoring force model of STHCCs are established by statistical regression.

In order to investigate the bearing capacity of composite columns composed of ultra-high performance concrete, (UHPC)-filled high-strength elliptical steel tube with encased high-strength H-shape steel (HUCFESTCs) were subjected to eccentric load. Forty-four HUCFESTCs were designed with varying parameters: yield strength of the steel tube (f_y), yield strength of the H-shape steel (f_y1), concrete-cube compressive strength (f_cu), steel tube thickness (t), eccentricity (e), slenderness ratio (λ), the section area of the H-shape steel (A_HS), and long–short axis ratio (ψ). Based on a bilinear elastic–plastic constitutive model of steel that considered stress hardening and a nonlinear constitutive model of UHPC, 44 HUCFESTCs models were established by ABAQUS software. The influence of different parameters on the ultimate bearing capacity of the HUCFESTCs was analyzed. The whole process of HUCFESTCs under eccentric load was studied, and the typical failure modes of HUCFESTCs are described. The results show that the main failure mode of the HUCFESTCs subjected to eccentrical load is bulging outward of the steel tube, the buckling of the H-shape steel, and crushing of the concrete in the middle part of the column and the inner part of the H-shape steel. The stiffness of HUCFESTCs increases gradually with the increase in f_y, t, and e. The ultimate eccentrical compression bearing capacity of HUCFESTCs improves gradually with increases in f_y, t, f_y1, A_HS, ψ, and f_cu, but it decreases gradually with increases in λ and e. By using statistical regression and introducing the reduction coefficient of eccentricity, the calculation formula for the eccentric bearing capacity of HUCFEST columns is developed, which can provide a basis for the application of HUCFESTCs in practical engineering.