Internal Columns Research Articles

Application of 1-D and 2-D Discrete Wavelet Transform to Crack Identification in Statically and Dynamically Loaded Plates

The paper presents the problem of damage detection in thin plates while considering the influence of static and dynamic characteristics, especially with regard to the modes of vibration as well as the excitation by static loads. The problem of Kirchhoff plate bending is described and solved by the Boundary Element Method (BEM). Rectangular plates supported on boundary or plates supported on boundary and resting on the internal columns are examined. A defect is introduced by the additional edges forming a crack in the plate domain. The analyses of static and dynamic structural responses are carried out with the use of Discrete Wavelet Transform (DWT). Signal decomposition according to the Mallat pyramid algorithm is applied. To obtain a more adequate input function subjected to DWT the white noise disturbing the signal is considered together with the structural response. In the dynamic experiments the plate undergoes vibrations similar to natural modes. The measured variables are static deflections and vertical displacement amplitudes. All of them are established at internal collocation points distributed alongside the line parallel to selected plate edge.

Dynamic performance of a real-scale reinforced concrete building test under a corner-column failure scenario

The topic of robustness and progressive collapse of structures has attracted significant attention within the field of structural engineering recently. This is reflected by the rise in the number of scientific papers published in recent years as well as efforts in reviewing and developing codes for design. Although important numerical and experimental studies have been carried out to date simulating the sudden removal of columns to reproduce the possible consequences of an extreme event, most of these studies focus on subassembly systems and internal columns. Edge and corner columns are most vulnerable to accidental events. This paper gives the results of a test carried out on a purpose-built full-scale reinforced concrete building with a specially designed corner steel column used for the sudden column removal. The test was highly instrumented, involving 38 strain gauges, 38 displacement transducers and 2 accelerometers to monitor the vertical and lateral response. The results were used to analyse the dynamic performance of the structure after the sudden column removal as well as the alternative load paths (ALPs) mobilised during the test (i.e. flexural and Vierendeel action). The test showed a clear dynamic amplification of the strains and displacements (with high peaks); dynamic amplification factors (DAFs) were obtained accordingly. The load initially carried by the removed column was redistributed through the entire building system (not just the neighbouring columns). Tests on full-scale buildings, including the one described here, can be used to compile a database to validate codes and future numerical studies.

Parametric analysis on punching shear resistance of reinforced-concrete continuous slabs

Punching shear resistance formulations provided by codes are usually calibrated on test results of isolated specimens that typically simulate the slab zone within the points of contraflexure around the column (hogging area). However, the behaviour of actual continuous flat slabs can be different to that of isolated specimens owing to the beneficial contributions of moment redistributions and membrane actions that cannot take place in isolated specimens. This paper presents a parametric study carried out to highlight the influence of the main geometrical features and the reinforcement layout affecting the punching shear resistance of continuous slabs around internal columns.

Analytical Study of Flat Slab Collapse Mechanisms due to Overloading in a Cluster of Exterior Panels

Analytical equations found in the literature to give the ultimate load of folding, punching shear and local slab collapse mechanisms have been generally derived assuming a uniform load on all flat slab panels. Regarding that these formulas are not able to consider the impact of unbalanced bending moment due to partial loading, they cannot be applied to evaluate scenarios like overcrowding during operation and change of occupancy. This paper categorizes various collapse modes due to overloading in a cluster of exterior panels as well as presenting analytical equations for the ultimate loads using virtual work method and yield line theory. The study also introduces two novel local slab collapse patterns around interior columns located at the corner of overloaded area. Predicted ultimate loads indicate that flat slabs on a square column grid are expected to be more prone to punching shear and asymmetric local modes around the internal columns supporting two adjacent overburdened panels compared to other column locations.

Numerical Evaluation of Progressive Collapse Potential in Reinforced Concrete Buildings with Various Floor Plans Due to Single Column Removal

Progressive collapse is defined as the spread of an initial damage from one member to another, leading to extensive partial or total collapse of the structure. In this research, the potential of progressive collapse due to a sudden removal of vertical load-bearing elements in reinforced concrete buildings structures with different floor plans such as geometrical regular and irregular floor plans as well as floor plans with and without torsional irregularity were assessed. The buildings were designed according to ACI 318-14 provisions and Iranian seismic code. The progressive collapse potential of the structures was assessed following of a sudden column or shear wall removal in different locations in their first floor using nonlinear dynamic analysis (NDA). Displacement sensitivity and column sensitivity indexes were utilized to compare different cases of load-bearing element removal in each model. Results indicated that in all geometrical regular floor plan, floor plan with reentrant corner and floor plan with torsional irregularity, the most critical case of column removal was removing columns located in outer corners of the plan. In addition, removing external columns was more critical than internal columns. In buildings with shear walls, removing shear walls led to much more critical scenarios than removing columns. Furthermore, results revealed that buildings with torsional irregularity floor plan, designed according to Iranian seismic code, had a lower potential of progressive collapse rather than those buildings with no irregularity.

Design of punching shear for prestressed slabs with unbonded tendons on internal columns

ABSTRACT This paper is related to the punching shear in prestressed slabs with unbonded tendons for interior columns calculated by the codes ABNT NBR 6118:2007, ABNT NBR 6118:2014, EN 1992-1-1:2004 e ACI 318-11. To calculate the punching shear resistance the formulations of the NBR 6118:07, effective until April/2014, did not consider the compression of the concrete in the plane of the slab, due to prestressing. Just the inclined components of some tendons were considered for total load applied relief, but this fact did not generate a significant difference, compared to reinforced concrete, because the inclination angle is very close to zero. The American and European provisions consider a portion related to the compression of the concrete in the planeof the slab. Differences in the results obtained by the four design codes will be exposed, showing that the EC2:04 and the NBR6118:14 achieved the best results.

Assessing the suitability of a green solvent for gel permeation chromatography–mass spectrometry analysis

ABSTRACTThe study presents the possibility of performing the analysis of oligomeric structures and polymer additives by gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) in dibuthoxymethane (DBM, butylal), a halogen-free and less hazardous solvent than typically used chloroform and tetrahydrofuran. Polystyrene oligomers and Irganox® additives were analyzed in DBM using 2.1 mm internal diameter GPC columns, allowing to decrease the flow rate down to 50 µL/min, compatible with APCI–MS interface. The ionization was controlled by adding 1% chloroform in DBM to obtain (M+Cl)− adducts, allowing a fast optimization of method parameters.

Analysis of the collapse of a greenhouse with vaulted roof

The failure of a multi-span steel greenhouse with vaulted roof covering an area of 7500 m2 is analysed numerically. Failure occurred during a day of heavy snow and moderate wind. The weather data at the location of the greenhouse and at the time of the collapse were not recorded. Weather data were available from meteorological stations in the broader area though. Numerical models of the complete 3-D structure and of a representative 2-D frame were developed to simulate the greenhouse structural behaviour under various combinations of actions. Linear, geometric and material nonlinear analyses were employed to investigate the causes of collapse. Based on the relevant provisions of the European Standard for greenhouse design and the Eurocodes, loading was varied to allow for an estimation of the real loading conditions at failure. Analysis confirmed the in- and out-of-plane failure modes that were observed after the incident. Based on all available data and the analysis results, it was shown that failure was the result of the combination of many factors that occurred simultaneously: an unfavourable combination of snow and wind actions, the heating system not operating as it should under such weather conditions and the absence of a complete row of internal columns.

Analysis of Reinforced Concrete 3d Frame under Blast Loading and Check for Progressive Collapse

Objectives: The main objective of this paper is to prevent the structures from blast loading and familiarize with design methods followed as per UFC guidelines. To prevent from these extreme loads we have adopted alternate path method for design. Methodology: Blast loads are generally dynamic in nature, so that it varies with time comprising of two phases namely positive phase and negative phase. In this paper for analysis of structure, we have considered only positive phase for the analysis. The load is applied as a triangular impulse loading as a time history variant neglecting the negative phase of the loading. The numerical model of this structure is created and analysed using the STADD. Pro software. The load values required for the model are obtained from IS:4991, the blast parameter values are found for a standoff distance of 20m,30m and 40m by varying charge weight as 100KG, 500KG and 1000KG. Analysis is carried out for different grades of concrete in STADD. Pro and results are compared and analysed. Progressive collapse is also checked by providing plastic hinges in the structure as per FEMA 356 provisions using SAP2000 as per UFC guidelines. Findings: The alternate approach followed shows the structure is safe by removing columns at different positions. The results obtained shows the plastic hinges formed in the corner column are higher compared to any internal columns. Improvements: Further improvements adopted can be by applying special design for reinforcements apart from general design.

Recent Advances in the Technologies of Connection for Panel Structures: Development of an Hysteretic Damper for Industrial Buildings

Background: The most recent seismic events occurred in Italy have highlighted some of the drawbacks of precast concrete industrial buildings and especially those related to the connecting systems traditionally employed to fasten the cladding panels to the internal framing. In fact, in many cases, the out-of-plane collapse of the external walls has been observed due to the problems related to the poor behaviour exhibited under cyclic loads by the connectors used to join the panels to the perimeter beams. Objective: In light of these outcomes, in this work, the possibility to improve the traditional structural details of industrial buildings by proposing the adoption of a dual system composed by the internal pendular columns and the external walls is examined. Method: It is provided to substitute the joints classically adopted at the top of the walls with a connection able to work as a slider with vertical axis and to insert at the bottom of the walls two or more hysteretic dampers recently patented at the Italian Patent Office after revision of the European Patent Office (EPO). With this approach, with respect to the classical design philosophy, due to the participation of the cladding panels, the structure is stiffened, obtaining an improved due to the additional source of energy dissipation represented by the dampers located at the base of the walls. Results and Conclusion: The effectiveness of the suggested approach is verified by evaluating the results of pushover analysis carried out on a building designed following the proposed approach.

An Innovative Dual System for New Structures or for the Retrofit of Precast Concrete Industrial Buildings

In this work, the possibility to improve the seismic behaviour of precast concrete buildings is examined by proposing the adoption of a dual system composed by the internal pendular columns of the building and the external cladding walls. To this scope, it is suggested to substitute the joints classically adopted at the top of the panels with a connection able to work as a slider with vertical axis and to insert at the bottom of the walls two or more hysteretic dampers working on the uplift of the cladding panels occurring under seismic actions. With this approach, with respect to the classical design philosophy, due to the participation of the cladding panels, the structure is stiffened, obtaining a reduction of the lateral drifts under serviceability limit states, and its seismic behavior is improved due to the additional source of energy dissipation represented by the dampers located at the base of the walls. The effectiveness of the suggested approach is verified on a case study designed following the proposed approach.

Comparison of punching shear requirements in BS 8110, EC2 and MC2010

This paper compares design provisions for punching shear at internal columns in the superseded British Standard BS 8110, Eurocode 2 (EC2) and fib Model Code 2010 (MC2010). MC2010 is based on the critical shear crack theory proposed by Muttoni, which relates shear resistance to the width of the so-called ‘critical shear crack’ which depends on slab rotation. Parametric studies are presented that show BS 8110 to require significantly less shear reinforcement within 1·5d (where d is the slab effective depth) of the loaded area than EC2 and MC2010, both of which have been extensively calibrated against test data. This raises the question of whether flat slabs designed to BS 8110 have an adequate factor of safety against punching failure. This question is explored using nonlinear finite-element modelling in conjunction with MC2010 Level IV. It is shown that punching resistance at internal columns can be increased significantly by restraint from the surrounding slab but the strength increase is variable and, in the case of uniformly loaded slabs, already largely included in BS 8110 and EC2.

Infilled masonry walls contribution in mitigating progressive collapse of multistory reinforced concrete structures according to UFC guidelines

A structure is subjected to progressive collapse when an element fails, resulting in failure of adjoining structural elements which, in their turn, cause further structural failure leading eventually to partial or total collapse. The failure of a primary vertical support might occur due to extreme loadings such as bomb explosion in a terrorist attack, gas explosion and huge impact of a car in the parking area. Different guidelines such as the General Services Administration (GSA 2003) and the Unified Facilities Criteria (UFC 2009) addressed the structural progressive collapse due to the sudden loss of a main vertical support. In the current study, a progressive collapse assessment according to the UFC guidelines is carried out for a typical ten-story reinforced concrete framed structure designed according to codes [(ACI 318-08) and (ASCE 7-10)] for minimum design loads for buildings and other structures. Fully nonlinear dynamic analysis for the structure was carried out using Applied Element Method (AEM). The investigated cases included the removal of a corner column, an edge column, an edge shear wall, internal columns and internal shear wall. The numerical analysis showed that simplification of the problem into 3D bare frames would lead to uneconomical design. It was found for the studied case that, the infilled masonry walls have a valuable contribution in mitigating progressive collapse of the reinforced concrete framed structures. Neglecting these walls would lead to uneconomical design.

ANALYSIS OF CYLINDRICAL SHELL STRUCTURE WITH VARYING PARAMETERS

The shell structures are composed of a thin shell made of reinforced concrete without the use of internal columns giving an open interior. Most common shells used in industry are flat plates and domes but different shapes like cylindrical, parabolic or spherical section may also used. Sports or storage facilities buildings are common concrete shell structures. However, they can be difficult to design, as the exact shape required for stability of structure depends on the material used, the size of the shell, exterior or interior loading, and other oblique. So by varying the parameter of the shell, behaviour of the shell is also varying. Main goal of this paper is parametric analysis of the multiple cylindrical shell structures with different lengths. For analysis we took two different lengths of cylindrical shell and then, two parameters have been change first one is radius and second is thickness, on the basis of different radius and thickness for same chord width, length, and material of shell we will compare the behaviour of shell for different models.

Shear resistance of reinforced concrete waffle flat slabs around the solid panel

This work presents a study on the behaviour of reinforced concrete waffle flat slabs with solid panels around internal columns and without moment transfer. Testes on 6 square waffle flat slab models were carried out, with 2400 mm in side length, 185 mm in height, 70 mm in top slab thickness, 115 mm in ribs height, 50 mm in ribs width, and 270 mm in ribs spacing, from center to center. The variables were the size of the solid panels (either 590 × 590 mm or 1130 × 1130 mm), ribs web steel ratio, type and layout. Except for one model that failed in flexure by crushing the ribs at the solid panel, all other models failed in shear by diagonal tension of the ribs. Test results were analyzed and compared with one another and with the estimations of existing expressions from codes and from other works available in the literature for punching shear of the solid panels around the column and ribs shear next to the solid panels. Finally, proposals for the design procedures for the slab region within the lines of zero moments and around the columns are given, regarding the definition of the solid panel size as a function of the ribs resistances towards shear and flexure.

The MYB46/MYB83-mediated transcriptional regulatory programme is a gatekeeper of secondary wall biosynthesis.

The secondary cell wall is a defining feature of xylem cells and allows them to resist both gravitational forces and the tension forces associated with the transpirational pull on their internal columns of water. Secondary walls also constitute the majority of plant biomass. Formation of secondary walls requires co-ordinated transcriptional regulation of the genes involved in the biosynthesis of cellulose, hemicellulose and lignin. This co-ordinated control appears to involve a multifaceted and multilayered transcriptional regulatory programme. Transcription factor MYB46 (At5g12870) has been shown to function as a master regulator in secondary wall formation in Arabidopsis thaliana. Recent studies show that MYB46 not only regulates the transcription factors but also the biosynthesis genes for all of the three major components (i.e. cellulose, hemicellulose and lignin) of secondary walls. This review considers our current understanding of the MYB46-mediated transcriptional regulatory network, including upstream regulators, downstream targets and negative regulators of MYB46. MYB46 is a unique transcription factor in that it directly regulates the biosynthesis genes for all of the three major components of the secondary wall as well as the transcription factors in the biosynthesis pathway. As such, MYB46 may offer a useful means for pathway-specific manipulation of secondary wall biosynthesis. However, realization of this potential requires additional information on the 'MYB46-mediated transcriptional regulatory programme', such as downstream direct targets, upstream regulators and interacting partners of MYB46.

The experimental investigations of RC internal columns in the connection zone with lightweight concrete slab

This paper presents the problem of load carrying capacity of the columns made of high-strength reinforced concrete which are separated by slab made of lightweight concrete. The experimental investigations of three models representing the internal connection between column and flat slab made of lightweight concrete of the strength tree times less than concrete strength of column are presented. The effort degree on the punching shear capacity stands for the variable parameter in the presented study. The performed study shows that there is no effect of this parameter on the effective concrete strength of the column.

Free vibrations of arbitrary quadrilateral thick plates with internal columns and uniform elastic edge supports by pb-2 Ritz method

Free vibration analysis of arbitrary quadrilateral thick plates with internal columns and elastic edge supports is presented by using the powerful pb-2 Ritz method and Reddy\'s third order shear deformation plate theory. The computing domain of arbitrary quadrilateral planform is mapped onto a standard square form by coordinate transformation. The versatile pb-2 Ritz functions defined by the product of a two-dimensional polynomial and a basic function are taken to be the admissible functions. Substituting these displacement functions into the energy functional and minimizing the total energy by differentiation, leads to a typical eigenvalue problem, which is solved by a standard eigenvalue solver. Stiffness and mass matrices are numerically integrated over the plate by using Gaussian quadrature. The accuracy and efficiency of the proposed method are demonstrated through several numerical examples by comparison and convergency studies. A lot of numerical results for reasonable natural frequency parameters of quadrilateral plates with different combinations of elastic boundary conditions and column supports at any locations are presented, which can be used as a benchmark for future studies in this area.

Progressive collapse assessment of framed reinforced concrete structures according to UFC guidelines for alternative path method

A structure is subjected to progressive collapse when a primary vertical structural element fails, resulting in failure of adjoining structural elements which, in their turn, cause further structural failure leading eventually to partial or total collapse. The failure of a primary vertical support might occur due to extreme loadings such as bomb explosion in a terrorist attack, gas explosion and huge impact of a car in the parking area. Different guidelines such as the General Services Administration (GSA) and the Unified Facilities Criteria (UFC) addressed the structural progressive collapse due to the sudden loss of a main vertical support. In the current study, a progressive collapse assessment according to the UFC guideline is carried out for a typical 10-story reinforced concrete framed structure designed according to (ACI 318-08). Fully nonlinear dynamic analysis for the structure was carried out using Applied Element Method. The investigated cases included the removal of a corner column, an edge column, an edge shear wall, internal columns and internal shear wall. The numerical analysis showed that for economic design, the slabs should be taken into consideration due to their significant effect on structural integrity after support removal. The simplification of the problem into 3D bare frames would lead to uneconomic design. It was found for the studied case that, reinforced concrete structures designed according to ACI code does not meet the UFC limits and that they a have a high potential for progressive collapse for cases of loss of either the corner column or edge shear wall. A modification for the ACI code was proposed to meet the UFC limits.

Effect of wind loading on spherical single layer space truss steel domes

The use of space truss steel domes has been a popular choice for covering large span areas with or without internal columns. High structural stiffness and architectural aesthetics are the main reasons for the wide application of this space truss form. Using formex algebra, the geometry of ribbed and Schwedler single layer space truss domes for various rise-to-span ratios (with a constant span) are modeled. Wind pressure, according to the American National Standards Institute (ANSI) code and the European Convention for Constructional Steelwork (ECCS) are applied to the surfaces of the models. To investigate the effect of wind load when compared with other loads, the uniform dead load applied on models and the results of the analyses in the fields of the node displacement, support reaction, overturning moment and sliding of foundation were compared with each other. Key words: Schwedler domes, single layer space truss dome, formex algebra, ribbed domes, wind pressure.