Floor Column Research Articles

An Investigation of the Effect of Semi-rigid Connections on Sudden Column Removal in Steel Frames

The semi-rigid behaviour of beam-to-column connections has an important effect on the performance of steel frame. This paper proposes a multi-spring component (MSC) model for assessing the rotational stiffness of semi-rigid beam-to-column connections. The main benefit of the MSC model is its ability to easily determine the response of semi-rigid beam-to-column connections in frame analysis. The MSC model is first validated through comparisons with 3D finite element method modelling and experimental test results, where good agreements of load rotation responses are generally observed. Then, using the MSC model, the semi-rigid connections in the frame were modelled by using rotational springs, and the ground floor columns were suddenly removed in sequence. The response of the remaining frame to this sudden removal was obtained through numerical simulation. The results of this simulation showed that the effect of the semi-rigid connection is crucial in the load-distribution and the frame deformation, and the influences of the column loss location and column removal time on frame response were discussed. The MSC model is design-effective and hand-calculable, and thus it brings convenience to the robustness assessment of steel frames suffering single column loss with considering semi-rigid connection and catenary action.

Effects of drying and rewetting on soluble phosphorus and nitrogen in forest floors: An experiment with undisturbed columns

AbstractDrying and rewetting (D/W) of soils often resulted in the release of soluble phosphorus (P) and nitrogen (N), thereby changing the availability of both nutrients. Most experiments on D/W have been conducted with disturbed mineral soil samples and with rewetting of the soil samples by abrupt change in the water potential. Here, we studied the effect of D/W on the leaching of P and N from undisturbed forest floors of a European beech and a Norway spruce site under near field conditions of desiccation and rewetting. We hypothesized that even under realistic rewetting of undisturbed forest floors, the leaching of P and N is increased after D/W and that the effects are less pronounced for spruce than for beech because of the larger hydrophobicity of the spruce forest floor. Undisturbed forest floor columns were subjected to desiccation at 20°C until a matrix potential of –100 MPa (pF 6.0) was reached, while controls were kept at moist conditions. Columns were irrigated by 22 mm day−1 from day 1–3 and by 10 mm day−1 from day 4–14 given in automated short pulses. Leachates from the soil columns were analyzed for orthophosphate, total P, NH4, NO3, and total N. In the spruce forest floor the concentrations of total P in leachates and the leachate fluxes were strongly increased after D/W. The increase of solute P was less for beech than for spruce coinciding with less actual rewetting of the beech forest floor. Leaching of total N from the spruce forest floor was not affected by D/W, however, concentrations and leaching of NH4 increased, while leaching of NO3 decreased. For beech the leaching of total N and NH4 increased after D/W, while NO3 leaching decreased. The results indicate that also under realistic conditions, D/W of forest floors increases solute P and leads to changes in the ratio of NH4/NO3 in solution, thereby altering the availability of the nutrients.

Experimental study on reinforced concrete frames with two-side connected buckling-restrained steel plate shear walls

This article experimentally studies the seismic behavior of reinforced concrete frames with buckling-restrained steel plate shear walls. The buckling-restrained steel plate shear wall is connected to adjacent reinforced concrete beams alone by an embedded steel connector in the beams (two-side connection). This is to avoid the force transfer between the shear wall and adjacent columns with a four-side connection. Four specimens of two-story and one-bay reinforced concrete frames with buckling-restrained steel plate shear walls are designed and tested under monotonic and cyclic loads. Finite element analyses are also conducted to further investigate the advantages of buckling-restrained steel plate shear walls by comparing the behavior of reinforced concrete frames with and without buckling-restrained steel plate shear walls. The results show that the presence of buckling-restrained steel plate shear wall can not only enhance the stiffness and load-bearing capacity but also improve the ductility and energy dissipation capacity of reinforced concrete frame structures. It is found that the drift ratio of the specimens reaches 1/15 under monotonic loads and 1/30 under cyclic loads. The specimens have ductility coefficients greater than 10. Two failure modes are found for reinforced concrete frames with buckling-restrained steel plate shear walls. Damages may concentrate at the base of ground floor columns for a frame with strong connectors, while plastic hinges may form at the ends of beams and columns for frames with weak connectors.

Investigating Performance of Plastic Hinge in Steel Frames by Knee Bracing

Constructing plastic hinges and the way of their distribution and failure mechanism can play an important role on seismic structures design. Mechanism type affect frame sensitivity toward secondary effects, total and local ductility, energy absorption and structure resistance before damage, general instability and destruction. Failure mechanism of moment frames under earthquake effect could be mentioned as three general types (first, second and third). The first type resulted from constructing hinges in beams and columns in the first few -story up, the second one resulted from constructing hinges in beams and columns of few upper -story and the third type including mechanism of one middle floor. Failure mechanism of general type is a special mode of the second type mechanism in which, plastic hinges locating at the two ends of beams and the first floor columns near the connection to the foundation. Based on researches, this type of mechanism shows the most amount of energy absorption against earth quack. Knee bracing frame is appropriate as an energy dissipation system composed of ductility and lateral stiffness which has good performance against lateral loads specially earthquake. In this paper, forming plastic hinges of components and the base shear of different steel systems and comparing them with knee bracing lateral load system in three, five and seven -story frames using regulations of FEMA356 and ATC-40.

Collapse Behavior of RCC Building under Blast Load

This investigation deals with the effect of intended explosion to a structural member. Due to such explosion, the load bearing structural member will be damaged and loses its load carrying capacity. This lead to formation of the critical path situation for transfer of load to the adjacent members. The study includes the investigation of critical columns for a 4 storey RCC building with 3×3 bays having longitudinal bay span of 5 m and transverse bay span of 4 m. The building is symmetrical throughout the height. The height of building is 3.5m at each floor except the ground floor of 4 m height. The behavioral changes have been investigated, under critical load path of the building subjected to a sudden collapse of load bearing member. This RCC building is designed as per relevant Indian codes and investigation is carried out considering the load path where maximum behavioral changes occur in terms of displacement, vertical reaction and axial forces after removal of load bearing member due to the blast load. The numerical investigation is carried out using commercially available software STAAD. Pro®. It is observed that ground floor columns are most critical for load transfer and joint displacement when subjected to blast loading. Further, based on the investigation exterior and interior critical columns are established after the removal of column due to blast load.

Degradation of Reinforced Concrete Structures of Aluminum Electrolysis Plants Subjected to Elevated Temperature and Cyclic Load

Technical papers describing the temperature related degradation of concrete are abundant, and serious damages often occurred in concrete structures subjected to high temperature such as metallurgy factories, although such occurrences were seldom made public. Concrete structures in aluminum electrolysis plants are generally subjected to high temperature emitted from electrolysis cells and cyclic load of heavy vehicles. Besides, hydrogen fluoride emitted from cells and stray current through reinforcement may cause deteriorating effects. In the case of an electrolysis plant built in Niigata in late 1960's, a part of passageway slab collapsed within a year of operation. A few years later, mesh shaped cracks on operation floor and shear cracks on floor beams and columns were observed. And an overall investigation on floor beams of 4 smelter buildings was carried out to determine the extent of deterioration, in 1972. The residual strength decreased linearly with operation term. The extent of strength reduction in "t" years' operation that we named "Deterioration Factor" and limit of lifetime were estimated. Countermeasures to reduce cyclic load and to reinforce floor beams were then taken, as well as the application of the Deterioration Factor to the next electrolysis plant in Shikoku Island. Details of renewed design of S-Electrolysis Plant and degradation of concrete are discussed. These aluminum electrolysis plants in Niigata and Shikoku have stopped operation in 1985 due to the withdrawal of the refining company, and existing smelter buildings have been diverted to another use. Although this paper presents rather retrospective cases, the authors wish this would be still helpful as a case study on degradation in concrete structure due to elevated temperature.

Stress-transfer in concrete encased and filled tube square columns employed in top-down construction

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

Design implications of a new load introduction mechanism into concrete-filled steel tubular columns

This paper presents the design implications of a new load introduction mechanism into concrete-filled steel tubular columns (CFST) proposed by the authors recently. According to the new load introduction mechanism, the beam-column connection load is introduced into the composite column through the column length above and within the connection. Based on the new load introduction mechanism, for slender CFST column design, a “concrete strength reduction factor” should be used to account for incomplete load introduction, when calculating the CFST column cross-section flexural stiffness. For CFST columns under combined axial compression and bending, the concrete strength reduction factor should be used when calculating the compression resistance, but should be ignored when calculating the bending resistance because composite action is always guaranteed for bending of the CFST column. The most important implication of the new load introduction mechanism is that the concrete core above the connection should be designed to resist the additional compressive force introduced to the concrete core below the connection. A further implication is that for ambient temperature design, the steel contribution ratio (steel section plastic resistance/plastic resistance of the composite cross-section) of the top floor column should be at least 0.25. For fire resistance design, the steel contribution ratio of the top floor columns, those on the floor below the top floor, and those two floors below the top floor, should not be less than 0.5, 0.33, and 0.25 respectively.

Structural response of RC frame under seismic loading by varying inclination angle of cross bracing

Structural performance is greatly affected by the use of concrete bracing in high seismic zone areas. A study representing the structural performance of a five-storey RC braced frame structure, by varying the inclination angle of concrete bracing, has been carried out by the use of numerical modelling for an earthquake load relating to a PGA value of up to 0.24 g. To investigate the problem, hypothetical models have been generated and analysed in SAP 2000 software using 3D modelling. Three models with different angle of bracing (i.e., < 45 degree, 45 degree and > 45 degree) are studied and compared with frame structure. Design considerations as per 'UBC-97' and 'BCP-2007' were used and response spectrum analysis has been carried out to observe the structural behaviour under dynamic loading. The parameters considered in this study are lateral displacements, inter-storey drifts, time period, base shear forces and axial forces and bending moments in ground floor columns. It has been concluded that the bracing angle affects the overall performance of structure. RC braced frame model with bracing angle less than 45 degree gives better seismic performance in terms of lateral drift and forces in structural members.

Effects of Footfall Induced Vibrations on Concrete and Composite Floors

This paper investigates the effects of footfall induced vibrations on the floors of a 3-storey sub-frame structure. Composite and concrete floors were examined. Variables involved are floor widths, floor thicknesses, floor aspect ratios and column heights. Models are generated and analysed using the finite element method. The vibration responses were represented in terms of displacements and accelerations. Results show that higher vibration responses occurs on longer floor widths, thinner floor slabs and higher floor aspect ratios for both composite and concrete floors.

Progressive collapse mechanisms investigation of planar steel moment frames under localized fire

In this paper, the possible progressive collapse mechanisms of planar steel frames when one column failed under elevated temperature was studied through extensive case studies. An explicit dynamic solver was adopted, which could continue beyond local element buckling. The effects of analysis parameters such as mesh size and loading speed were investigated. And the numerical model was validated against experimental data and analysis results of other researchers. The investigated parameters included beam cross-sectional size, load ratio and location of heated column. Three progressive collapse mechanisms were found, namely, cantilever beam mechanism, pull-in force induced mechanism and high load ratio member failure mechanism, of which the last one is a new discovery. To evaluate progressive collapse of planar steel frames under fire, the cantilever beam mechanism and the pull-in force induced mechanism should be checked when the outer columns are heated, and the pull-in force induced mechanism and the high load ratio member failure mechanism need to be checked when the inner columns are heated. And the most adverse fire scenarios of a planer steel moment frame are when one of the following columns is heated: first floor column of the outmost, second and third outmost column lines or top floor column of the outmost, second and third outmost column lines.

Remaining service life estimation of reinforced concrete buildings based on fuzzy approach

The remaining service life (RSL) of buildings has been an important issue in the field of building and facility management, and its development is also one of the essential factors for achieving sustainable infrastructure. Since the estimation of RSL of buildings is heavily affected by the subjectivity of individual inspector or engineer, much effort has been placed in the development of a rational method that can estimate the RSL of existing buildings more quantitatively using objective measurement indices. Various uncertain factors contribute to the deterioration of the structural performance of buildings, and most of the common building structures are constructed not with a single structural member but with various types of structural components (e.g., beams, slabs, and columns) in multistory floors. Most existing RSL estimation methods, however, consider only an individual factor. In this study, an estimation method for RSL of concrete buildings is presented by utilizing a fuzzy theory to consider the effects of multiple influencing factors on the deterioration of durability (e.g., concrete carbonation, chloride attack, sulfate attack), as well as the current structural condition (or damage level) of buildings.

Effect of Bracing Systems on Fire-Induced Progressive Collapse of Steel Structures Using OpenSees

This paper investigates the effect of various bracing systems on the fire-induced progressive collapse resistance of steel-framed structures using OpenSees. Two types of bracing systems (vertical and hat bracing) and various fire scenarios (single and multi-compartment fires) are considered. Four collapse mechanisms of steel frames in fire are found through parametric studies. General collapse is characterized by the collapse of the heated bay followed by lateral drift of adjacent cool bays. Global collapse of a whole frame is due to the buckling of ground floor columns. Another two lateral collapse modes (local and global) are caused by catenary action developed in the heated beams under large deflections. Vertical bracing systems have positive effects on increasing the lateral restraint of the frame against local or global drift, while when arranged at edge bays of frames they negatively contribute to the spreading of a local damage to global collapse in the form of sequential buckling of adjacent columns through load-transfer mechanisms. For a more realistic arrangement of vertical bracings inside the frame, the bracing acts as a barrier to restrain the spread of local damage to the rest of the frame. Instead, using hat bracing can effectively optimize the load-transfer path through a more uniform redistribution of loads in columns and enhance the resistance of structures against progressive collapse. It is found that the application of vertical bracing systems alone on the steel frames to resist progressive collapse is proved to be unsafe and a combined vertical and hat bracing system is recommended in practical design.

Effects of confinement reinforcement and concrete strength on nonlinear behaviour of RC buildings

This paper investigates the effects of confinement reinforcement and concrete strength on nonlinear behaviour of reinforced concrete buildings (RC). For numerical application, an eleven-storey and four bays reinforced concrete frame building is selected. Nonlinear incremental static (pushover) analyses of the building are performed according to various concrete strengths and whether appropriate confinement reinforcement, which defined in Turkish seismic code, exists or not at structural elements. In nonlinear analysis, distributed plastic hinge model is used. As a result of analyses, capacity curves of the frame building and moment-rotation curves at lower end sections of ground floor columns are determined. These results are compared with each other according to concrete strength and whether appropriate confinement reinforcement exists or not, respectively. According to results, it is seen that confinement reinforcement is important factor for increasing of building capacity and decreasing of rotations at structural elements.

A Study on the Effect of Compartment Fires on the Behaviour of Multi-Storey Steel Framed Structures

In order to ensure safe evacuation of occupants and safe access for fire-fighters, current fire precautions aim to prevent fire spreading beyond the compartment where it started. The focus of this study is to assess the stability of structural components when localised fires occur in unprotected steel buildings. A three-storey three-bay symmetrical steel frame representing a typical office building was analysed using a finite element computer program. The influence of six different localised fire scenarios was investigated. For each fire scenario, the variation in deflections, bending moments and axial forces, as the temperature increases, were monitored up to failure of the structure. The results indicate that thermal expansion of the heated beams, leading to lateral movement of surrounding structural components, is an important factor. The resistance to this movement by the columns and general surrounding elements, which are not exposed to the fire, has a great influence on the redistribution of internal stresses. In general, this may lead to instability of columns, catenary action developing in beams, and eventually failure of the structure as a whole. The study suggests that critical localised fire scenarios are those where all the ground floor columns are affected, or where a whole bay through the height of the frame is heated. However, it has been shown that fire survival under any localised fire scenario is improved in comparison to that when the whole frame is heated. Therefore, fire compartmentation does not only provide safe means of escape, it is also beneficial for enhanced structural fire resistance.

Experiment on Seismic Behavior of Frame with Specially Shaped Columns Used Wide Flange in the First Floor and General on the above

Studies show that the stiffness of the first floor column about concrete frame with general specially shaped column is insufficient, the column bottom will be compression damaged easily, the author advice using wide flange specially shaped column in the first floor to enhance the stiffness, so this paper designed a 1/3 scale RC frame with specially shaped columns used wide flange in the first floor and general on the above, furthermore the height of the first floor was higher than other floors. Then low frequency cyclic loading was experimented to the concrete frame, the seismic behavior of this kind frame such as damage characteristic, failure mechanism, bearing capacity, deformation capacity, hysteresis curve and storey drift were researched. It was shown that the seismic behavior of this structure was generally good, the method that changed the first floor to wide flange specially shaped column for concrete frame with specially shaped columns could enhance the stiffness of the first floor clearly, meanwhile the seismic behavior of the frame were improved.

Numerical Seismic Performance of an Innovative CFS Midrise Building Designed Using DDD

AbstractLight-gauge cold-formed steel (CFS) is being used more and more as an economical and high performing construction material. In this paper, a numerical study of the seismic performance of an innovative light-gauge cold-formed steel midrise building designed using direct displacement design (DDD) is presented. This new system, termed a uniform truss construction system (UTCS), includes floor trusses, open panels, v-braced panels, columns, and connections between components. A series of reversed-cyclic tests of subassembly structures was conducted to provide the key information to understand the performance of the system under cyclic loading. The test data was then integrated into a numerical model for nonlinear time history analysis. A simplified shear element was developed to represent the panels as well as the floor diaphragm in the numerical model of the system. Nonlinear time history analysis of the building was conducted using a suite of 22 prominent earthquakes recorded from around the world. ...

Study on Design Measure of Seismic Capacity Design in R.C. Mega-Frame Structures

This paper explores the design method of several typical mega plane frames, with the variables being the combination of varying amplification coefficient of moment at bottom sections of ground floor columns of the secondary frame on the main beams. The elastic-plastic dynamic analysis program Drain-2d+ of the plane structure is used to carry out the elastic-plastic time-history analysis for each typical mega-frame under the earthquake action. Based on the analysis, the deformation characteristics of the mega-frame, the emerging of the plastic hinge and the weak point of the overall structure under the earthquake action is developed, from which the correct method of obtaining the design value of amplification coefficient of moments at bottom sections of ground floor columns of the secondary frame on the main beams is concluded. The reasonable design values are recommended as the basis to provide some suggestions for the design of the reinforced concrete mega-frame structure.

Progressive Collapse-Resisting Mechanisms of Reinforced Concrete Structures and Effects of Initial Damage Locations

Computational simulations for analyzing progressive collapse resistance of structures following initial damage require specific attention to structural modeling of floor systems. In collapse analysis of RC structures, it is shown that the degrees of freedom of nonlinear beam, joist, and slab sections must include flexural and axial deformations. It is also shown that ignoring torsional cracking of beams can lead to a significant overestimation of the progressive collapse resistance of structures. Evaluating the response of a seven-story RC structure following 15 simulated single column removal scenarios, it is shown that a top floor column removal is more likely to cause structural collapse than failure on a lower floor. This is in part due to the lack of Vierendeel frame action after a top floor column removal. For the simulated scenarios in which the structure resists progressive collapse without experiencing large vertical displacements, the resistance is primarily provided by Vierendeel frame action and axial compressive force-moment interaction of beams. The importance of the floor system in-plane action in axial-flexural response of beams is discussed. The effect of accounting for the elevation difference between the centerlines of floor slabs and beam elements within the building model is studied.

Three-Dimensional Effects and Collapse Resistance Mechanisms in Steel Frame Buildings

AbstractThis study investigates the robustness of a seismically designed steel moment frame building using 3-D nonlinear models. Computational simulations are carried out using validated models to investigate building response to loss of internal and external columns as well as columns in lower, middle and upper floors. Studies are conducted to gain insight into the sources of collapse resistance of the prototype building, focusing in particular on the role of composite action between the slab and underlying steel beams and slab membrane action. The simulation results suggest that the prototype building can be more vulnerable to loss of columns in the upper stories than in the lower ones and is particularly vulnerable to loss of interior gravity columns at all floor levels. The role of the slab is quantified and it is shown that it can contribute significantly to the robustness of the structure, but it is a double edge sword that can also be detrimental, especially in the final stages of collapse.