Stiff Steel Research Articles

Seismic Repair and Retrofit of RC Beam–Column Joints Using Stiffened Steel Plates

Evidence from past earthquakes has shown that during significant events, there are always a number of structures that stay stable but experience different forms of damage in their members. Among these members, beam–column joints in the moment frames are more susceptible to seismic loading and may experience different modes of failure. In this paper, stiffened steel plates are used to repair and retrofit a full-scale damaged RC beam–column joint. The retrofit method is based on joint enlargement. A full-scale external beam–column joint is designed and constructed as an ordinary moment resisting frame based on ACI 318M-11 provisions. The structure is then subjected to progressive quasi-static cyclic loading to failure. The damaged joint is then repaired to its former configuration using pressurized epoxy resin and retrofitted by stiffened steel plates. The repaired and retrofitted joint is then subjected to the same cyclic loading protocol to failure. Seismic performance parameters such as strength, stiffness, ductility and energy dissipation capacity of the original joint and the repaired and retrofitted joint are then extracted from their capacity backbone curves and compared. Results show that the proposed repair and retrofit technique not only regenerated the original capacity but also increased capacity and improved the joint performance by relocating the plastic hinge beyond the repaired region.

Response of pipelines of differing flexural stiffness to normal faulting

Relative ground movement represents a severe seismic hazard to pipelines crossing faults, and the maximum expected pipeline strains are the primary design concern. Past research has documented how stiff steel pipelines respond to permanent ground deformation and has produced calibrated empirical models of pipeline response to strike-slip and normal faulting. However, what little data exist on flexible pipelines illustrate how ‘stiff pipeline’ soil reaction models significantly overestimate peak strains for flexible pipelines. Results for four centrifuge tests conducted on model pipelines are presented to quantify the flexural response of pipelines to normal faulting over a wide range of pipeline stiffness. Continuous functions of pipeline and soil displacement calculated using digital image correlation are used to assess pipeline curvature, soil reaction and relative displacement. Comparisons of peak measured curvatures to current design analysis methods confirm that empirical stiff pipeline soil reactions progressively overestimate maximum curvature as the pipeline's stiffness decreases. Two strategies to modify current empirical soil reactions to account for flexible pipelines were then investigated, with the strategy of reducing the stiffness of the empirical soil reaction (while maintaining the advantage of a simplified, abrupt, step-like fault) providing better outcomes than modification to account for more realistic ground displacement profiles.

Nanoscale triboactivity of functionalized c-Si surfaces by Fe+ ion implantation

In the present work, we present a study of the effect of Fe+ ion implantation on the tribological response at nanoscale contact lengths of crystalline silicon (c-Si) surfaces. (1 0 0) silicon wafers were implanted with Fe+ at a fluence of 2 × 1017 cm−2, followed by annealing treatments at temperatures of 800 °C and 1000 °C. After microstructural characterization, nanoabrasive wear tests were performed with an atomic force microscope (AFM) using an AFM diamond tip with a stiff steel cantilever that enables the application of loads between 1 μN and 8 μN. After the nanowear tests, the same AFM was used to visualize and measure the worn craters. It was observed that the as-implanted samples present the poorest nanowear response, i.e. the highest wear rate, even higher than that of the unimplanted Si wafers used as a reference. Nevertheless, annealing treatments result in a measurable increase in the nanowear resistance. In this way we show that Fe+ ion implantation of c-Si, followed by the proper post-heat treatment, results in the formation of FeSi2 nanoprecipitates finely dispersed in a recrystallized matrix. This can be a valuable way of optimizing the nanotribological behavior of silicon.

Experimental and Simulation Study on Seismic Behavior of Beam-Column Joints with Cast Steel Stiffener

AbstractA series of six full-scale cruciform H-shaped beam to square tube column joint with cast steel stiffener specimens was tested under cyclic loading to study the seismic behavior of the new joints. A parametric numerical analysis based on the test results was also conducted. The hysteretic curves of specimens not filled with concrete were full, and the ones of specimens filled with concrete were pinched. The maximum moment resistance of the joints filled with concrete in the column increased from 10 to 30% compared with that of the joints not filled with concrete. The energy dissipation coefficient of the joints not filled with concrete in the column varied from 2.681 to 3.585, whereas it changed from 1.892 to 1.711 for the joints filled with concrete when the width of the square tube column ranged from 300 to 500 mm. The results demonstrate that the joints with cast steel stiffeners have excellent moment capacity, deformation performance, and energy dissipation coefficients. The new joints could po...

창문 열관류율 저감을 위한 열교 저감형 보강재 연구

Steel stiffener is required for reinforcing the structure of the window frame made of versatile but weak PVC material. Steel stiffener however becomes a source of greater heat loss and frequently plays a role of thermal bridge due to its high thermal conductivity. To maintain thermal resistance similar to PVC frame, steel stiffener is perforated to reduce the effective heat transfer area. To compensate the structural strength of the steel stiffener which is weakened by the perforation, the thickness is increased. Increase in thickness will also increase the thermal heat resistance. Five samples which are PVC frame, PVC frame + original steel stiffener, PVC frame + 30% perforated steel stiffener, PVC frame + 50% perforated steel stiffener, PVC frame + 65% perforated steel stiffener are modeled and simulated for 2nd moment of area and thermal resistance. Therm/window version 6.3 is used for thermal analysis. The results show that among the five samples analyzed, PVC frame + 65% perforated steel stiffener best satisfies both structural strength and thermal resistance.

Comparisons of buckling-to-weight behavior of cylindrical shells with composite and metallic stiffeners

The present research deals with the study of buckling pressure-to-weight ratio of cylindrical shells with laminated ring stiffeners. The research introduces a strain energy formulation for laminated rings, in which each ring stiffener may be treated individually and the geometrical dimensions and material properties of the stiffeners may be different from one another. In a parametric study, the impacts of various geometrical parameters of rings on the buckling pressure-to-weight ratio of shells for composite and metallic stiffeners are compared. The results show that the buckling-to-weight behavior of the shells with Steel stiffeners generally differs from the shells with stiffeners made of Aluminum, E-glass/epoxy, Graphite/epoxy, or Kevlar49/epoxy.

Experimental research on load-bearing capacity of cast steel joints for beam-to-column

The load transfer mechanism and load-bearing capacity of cast steel joints for H-shaped beam to square tube column connection are studied based on the deformation compatibility theory. Then the monotonic tensile experiments are conducted for 12 specimens about the cast steel joints for H-shaped beam to square tube column connection. The findings are that the tensile bearing capacity of the cast steel joints for beam-column connection depends on the ring of cast steel stiffener. The tensile fracture happens at the ring of the cast steel stiffener when the joint fails. The thickness of square tube column has little influence on the bearing capacity of the joint. The square tube column buckles while the joint without concrete filled, but the strength failure happens for the joint with concrete filled column. And the length of welding connection between square tube column and cast steel stiffener has little influence on the load-bearing capacity of the cast steel joint. Finally it is shown that the load-bearing capacity of the joints for H-shaped beam to concrete filled square tube column connection is larger than that of the joints for H-shaped beam to square tube column connection by 10% to 15%.

NONLINEAR ANALYSIS OF WITH AND WITHOUT STIFFENERS OF HOLLOW AND CONCRETE FILLED STEEL TUBE COLUMN BY USING ABAQUS 6.10-1

The concrete filled steel tube(CFST) column has got many advantages compared with the reinforced concrete member. Concrete filled steel tube are frequently used for piers, deep foundation, caissons and columns etc because of their high compressive strength and stiffness. Analytical Study of Hollow Steel Tube With concrete filled of different grades and without and with steel stiffeners (one stiffener and two stiffener) under monotonic loading is presented in this Paper. The nonlinear behavior of the columns is observed by using finite element software ABAQUS 6.10-1.the results from non linear finite element analyses is obtained and is verified with experimental tests, Eurocode Part-4 and ACI-318(2005).It was found that the non linear finite element simulations are in a good agreement with the codes of practice and experimental results. this study has carried out to examine the influence of several parameters such as thickness of tube(3mm and 4mm) and stiffener configurations(i,e At 1/3 times of height and 1/2 times of height), frequency , time period and also to find Ultimate load carrying capacity of hollow and composite column on the compressive response under axial load. The hollow and composite columns are extensively developed by considering different configuration of steel stiffeners. The main variables are: (1) number of stiffeners (2) arrangement stiffeners (3) stiffener spacing (4) thickness of steel tube (5) compressive strength of concrete(20MPa, 25MPa, 30MPa) .Effects of above variables mention on the behavior of columns is assessed. Failure modes and deformed shape of the columns is also illustrated. From this study it is concluded that, the developed finite element model gives closer perfection and depicts the non linear behavior well with 5-10% error. Also the non linear behavior is examine when only steel tube is loaded , only concrete is loaded and when both is loaded and the combination of loading on both steel tube and infill concrete gave higher load carrying capacity. The analytical results are well validated with previous researchers too.

Robustness of simple joints in pultruded FRP frames

Structural robustness of simple beam-to-column joints in pultruded frames is assessed through tension pull tests. The tying capacity and failure modes are determined from static tests on two batches of specimens for six joints. Tying resistance is an important joint property for maintaining structural integrity in frames in case of accidental loads. No tests have been previously reported to investigate this key structural property for the design of Pultruded Fibre Reinforced Polymer (PFRP) structures. The tension pull tests consist of a PFRP Wide Flange (WF) section bolted to a stiff steel baseplate by a pair of PFRP web cleats, and at the other end the tensile load is applied. One batch of three specimens has a WF 254×254×9.53mm section with 100×9.53mm cleats of equal leg-angle material and the other has a WF 203×203×9.53mm with angles of size 75×9.53mm. Tension versus displacement curves are plotted to establish linear-elastic response, damage onset, non-linear response and ultimate tensile strength. Damage initiation is characterised by audible acoustic emissions. The load–displacement curve remains linear elastic up to 0.35 to 0.4 of the maximum (ultimate) tension force and damage happens at 0.6 of the ultimate value. Failure is from excessive delamination cracking emanating in the region of a cleat's fillet radius. A model to predict tying resistance is proposed, and successfully calibrated against experimental results. The most important finding of this study is that a pair of 9.53mm thick PFRP leg-angle web cleats should possess an adequate tying capacity for design against disproportionate collapse.

Three-dimensional numerical modeling of hydrostatic tests of porous rocks in a triaxial cell

It is known that there is stress concentration at specimen ends during experimental rock tests. This causes a deviation of the measured nominal (average) stresses and strains from the actual ones, but it is not completely clear how strong it could be. We investigate this issue by numerical modeling of the hydrostatic tests using a reasonably simple constitutive model that reproduces the principal features of the behavior of porous rocks at high confining pressure, Pc. The model setup includes the stiff (steel) platens and the cylindrical model rock specimen separated from the platens by the frictional interfaces with friction angle ϕint. The whole model is subjected to the quasi-statically increasing normal stress Pc. During this process, the hydrostats Pc(ε) are computed in the same way as in the real tests (ε is the average volume strain). The numerical hydrostats are very similar to the real ones and are practically insensitive to ϕint. On the contrary the stresses and strains within the specimen, are extremely sensitive to ϕint. They are very heterogeneous and are characterized by a strong (proportional to ϕint) along-axis gradient, which evolves with deformation. A strong deviation of the stress state at the specimen ends from the isotropic state results in inelastic deformation there at early loading stages. It follows that the nominal stresses and strains measured in the experimental tests can be very different from the actual ones, but they can be used to calibrate constitutive models via numerical simulations.

Simulation Analysis on Hysteretic Performance of Cross-type Rigid Node for Steel Frame Based on Abaqus

In order to study the cross-type rigid steel frame node hysteretic behavior of components, the axial compression ratio, H type steel column web thickness, girder section and stiffener as design parameters, 8 steel frame cross-type rigid joints and a T-type rigid joint are designed. Based on simplified mechanical model and constitutive relations of material, using ABAQUS software the corresponding finite element model is established and the hysteretic performance analysis is carried out. Through comparison between given T-type node test results and analysis results, both are in good agreement, thus the rationality of the finite element model established in this paper is verified. Simulation analysis of cross-type node is developed in further, load -displacement hysteretic curve of nodes, skeleton curve, envelope figure and the stress nephogram are extracted and comparative analysis is conducted, influence regularity of four parameters on the seismic behavior of the joints is obtained. The corresponding design suggestion for the axial compression ratio and column web and flange thickness ratio is proposed, design limit value of axial compression ratio of column should be taken as 0.5 and limit value of column web and flange thickness ratio is taken as 0.75,and these can provide reference for actual engineering design.

Nonlinearities and self-organization in the sound production of the Rhodes piano

Over the last five decades the Rhodes piano became a common keyboard instrument. It is played in such diverse musical genres as Jazz, Funk, Fusion, or Pop. The sound processing of the Rhodes has not been studied in detail beforeIts sound is produced by a mechanical driven tuning fork like system causing a change in the magnetic flux of an electromagnetic pick up system. The mechanical part of the tone production consists of a small diameter tine made of stiff spring steel, the tine, and a tone bar made of brass, which is strongly coupled to the former and acts as a resonator. The system is an example for strong generator-resonator coupling. The tine acts as a generator forcing the tonebar to vibrate with its fundamental frequency. Despite of extremely different and much lower eigenfrequencies the tonebar is enslaved by the tine. The tine is of lower spatial dimension and less damped and acts nearly linear. The geometry of the tonebar is much more complex and therefore of higher dimension and damped stronger. The vibration of these two parts are perfectly in-phase or anti-phase pointing to a quasi-synchronization behavior. Moreover, the tonebar is responsible for the timbre of the initial transient. It adds the glockenspiel sound to the transient and extends the sustain. The sound production is discussed as synergetic, self-organizing system, leading to a very precise harmonic overtone structure and characteristic initial transients enhancing the variety of musical performance.

Numerical study of concrete-filled steel composite (CFSC) stub columns with steel stiffeners

Numerical study of concrete-filled steel composite (CFSC) stub columns with steel stiffeners is presented in this paper. The behaviour of the columns is examined by the use of the finite element software LUSAS. Results from nonlinear finite element analyses are compared with those from corresponding experimental tests which uncover the reasonable accuracy of the modelling. Novel steel stiffeners are used in the CFSC stub columns of this study. The columns are extensively developed considering three different special arrangements of the steel stiffeners with various number, spacing, and widths of the stiffeners. The main variables are: (1) arrangement of the steel stiffeners (C1, C2, and C3); (2) number of the steel stiffeners (2 and 3); (3) spacing of the steel stiffeners (50 mm and 100 mm); (4) width of the steel stiffeners (50 mm, 75 mm, and 100 mm); (5) steel thickness (2 mm, 2.5 mm, and 3 mm); (6) concrete compressive strength (30 MPa, 40 MPa, and 50.1 MPa); (7) steel yield stress ( 234.3 MPa, 350 MPa, and 450 MPa). Effects of the variables on the behaviour of the columns are assessed. Failure modes of the columns are also illustrated. It is concluded that the variables have considerable effects on the behaviour of the columns. Moreover, ultimate load capacities of the columns are predicted by the design code EC4, suggested equation of other researchers, and proposed equation of the authors of this paper. The obtained ultimate load capacities from the analyses are compared with the predicted values. It concludes that EC4 gives more conservative predictions than the equations.

Residual Stresses in Welded Stiffened Steel Plates—An Experimental Comparative Study

Abstract This paper examines the residual stress distributions at selected depths in three stiffened 350WT steel plates representing typical stiffened steel plates used in modern ship construction. Residual stresses can develop from the welding process, and the magnitude of these stresses can be high enough to cause an early onset of yielding. Therefore, fatigue or other failures can also occur when welding-induced residual stresses are combined with service-load-induced stresses. In this study, the welding-induced residual stresses of these stiffened steel plate specimens were quantified at the near surface using the X-Ray diffraction method and at various depths using the neutron diffraction method. Transverse and longitudinal stress components for all three specimens were collected and analyzed. The residual stress profiles determined from both methods were found to be similar. However, some disagreement was found within the heat-affected zone of the weld bead. This paper discusses the residual stress distributions found in the three specimens and compares the two methods of measurement.

Structural analysis of a steel double hull underwater tank, intended for oil recovery from shipwrecks

In the present work, the survivability of a submerged structure against loads, imposed by the operational environment, such as hydrostatic pressure is presented. The structure under consideration is a component (buffer bell) of a system called DIFIS that recovers fuel from shipwrecks. It consists of two parts: the reservoir and the floater. The floater is the part that produces the buoyancy force that holds the whole system in place and therefore its structural integrity is crucial for the safety of the structure. The floater is designed as a double hull structure made of steel plates and stiffeners. The task of the structural analysis is to ensure that the floaters’ double hulls are able to withstand the hydrostatic pressure due to the depth and maintain the needed buoyancy forces. In the present analysis, the strength of the hulls is evaluated for three different scenarios (operational, worst case and accident scenarios).

Observations from testing of indeterminate FRP-plated steel beams on flexible supports

This paper discusses the fabrication of, failure testing of and test data analysis from multiple two-span continuous FRP-plated steel I-beams. The study incorporated variation between beams of the layout and amount of FRP plating along the positive and negative moment zones, the novel concept of bonding (rather than welding) the steel plate stiffeners to the beams’ webs and flanges, use of longitudinal strain gauges on the bonded and exposed surfaces of key FRP plates, and elastomeric (hence flexible) pads to distribute stresses into the webs at the supports. The bonded steel stiffeners significantly delayed local buckling of the beams. Use of strains from only the exposed surface of any FRP plate produces erroneous magnitude changes and sign reversal of the high interfacial shear stresses near plate curtailment, relative to the prudent approach of using strain averages from the plate’s bonded and exposed surfaces. Differences between bonded and exposed surface strains enabled quantification of interfacial normal stresses. Relaxation of the rigid support assumption in favour of experimentally determined flexible support stiffnesses significantly nudges the predicted moment distributions toward the test distributions. This enables reliable assessment of the potential for end-peel failure arising from offsets between plate curtailment and contraflexure.

Analysis on Overall Design of the Main Bridge of Dalian South Binhai Avenue

The main bridge of Dalian South Binhai Avenue is a double-decked three-span earth -anchored suspension bridge with a full length of 820m, of which the main span is 460m, and a width of 24.8m. In this paper, the conceptual design of the steel stiffening truss girder, cable tower and anchorage are introduced and the design difficulties and points are analyzed. The anchorage adopts the hollow triangular frame structure, breaking through the physical heavy structure of gravity anchorage; and the design of two wedge-shaped gravel bed foundations improves the anti-slip safety factor of the anchorage. The offshore anchorage program provides a reference for the construction of future similar bridges.

Improved earthquake resistant design of torsionally stiff asymmetric steel buildings

In a companion paper as well as in earlier publications, it has been shown that in asymmetric frame buildings, designed in accordance with modern codes and subjected to strong earthquake excitations, the ductility demands at the so called flexible edges are consistently and substantially higher than the ductility demands at the stiff edges of the building. In some cases the differences in the computed ductility factors between elements at the two opposite building edges exceeded 100%. Similar findings have also been reported for code designed reinforced concrete buildings. This is an undesirable behavior as it indicates no good use of material and the possibility for overload of the flexible edge members with a consequent potential for premature failure. In the present paper, a design modification will be introduced that can alleviate the problem and lead to a more uniform distribution of ductility demands in the elements of all building edges. The presented results are based on the steel frames detailed in the companion paper. This investigation is another step towards more rational design of non-symmetric steel buildings.

Seismic Response Analysis of Double Chains Suspension Bridge Considering Non-Classical Damping

Damping in double chains suspension bridge is non-uniform, which leads to coupled motion equations in main coordinate system. Based on the complex damping theory to solve equivalent viscous damping ratio used to describe energy dissipation characteristics of non-classical damping system approximately, a method is proposed to analyze seismic response of double chains suspension bridge considering non-classical damping modified by measured value. Influence of different damping forms on seismic response of double chains suspension bridge is analyzed, considering classical damping and non-classical damping respectively, through an example of double chains suspension bridge. The analysis shows that non-classical damping has significant effect on seismic response, and response based on the classical damping model is not reliable to double chains suspension bridge. Non-classical damping model should be used in seismic analysis of double chains suspension bridge, however, the seismic response of non-classical damping system under the longitudinal or vertical seismic wave can be substituted approximately by the seismic response calculated according to damping ratio of concrete tower and steel stiffening girder respectively, which can simplify the calculation during preliminary analysis.

Prediction of welding deformations of large stiffened panels using average plastic strain method

Curved or flat stiffened steel panels used in ships and offshore structures are fabricated mainly by fusion welding. It leads to heat induced plastic strains, distortions and residual stresses. These distortions may adversely affect the subsequent fit-up and alignment of the adjacent panels. A solution methodology named average plastic strain method was developed and adopted based on evaluation of average plastic strains of butt and fillet joints of small scale specimens. These were obtained using the conventional thermomechanical analysis. These plastic strains were then used to determine the overall distortions of large stiffened plate panels. The results obtained were compared with those of established inherent strain method for prediction of distortion of large stiffened plate panels. Computational efficiency of the average plastic strain method was found to be comparable with the inherent strain method. However, the accuracy in the plastic strain method was found to be better than that in the inherent strain method.