Diaphragm Action Research Articles

Diaphragm action in light steel framing by sheathing boards

This paper presents the results of shear tests on light steel walls with two types of higher specification OSB/3 board and comparison with elastic theory based on the fixing shear stiffness. The tests were performed to BS EN 594 and showed that the design shear resistance was determined as 5.1 kN/m wall length for a limiting deflection of 0.003H or 4.3 kN/m for a limiting deflection of H/500, where H is the wall height. With plasterboard on the opposite face, the shear stiffness increased by 29%, but these results were more variable. For a single test on a wall with the OSB/3 board on one side and X bracing on the opposite face, the design shear resistance is 5.6 kN/m for a limiting deflection of H/500. For a flame retardant form of OSB/3 board, the stiffness was 21% higher than for the first series of OSB/3 tests. An elastic theory is presented to determine the limiting shear force as a function of the shear stiffness of the fixings between the boards and the C sections, which was provided from small-scale push tests. The results are compared with finite element models and a comparison with the test configurations is presented.

Augmenting the seismic performance of masonry models using polypropylene band and steel wire mesh through shaking table testing

The seismic vulnerability of unreinforced masonry (URM) structures was observed during the past seismic events, which caused a huge loss of life and property. However, URM buildings are quite common in developing countries like India as they offer cheap shelters to people with low income. An easily implementable strengthening technique with cost-effective materials for enhancement of the seismic behaviour of URM building is of utmost importance. Hence, this study was carried out to develop a technique to improve the strength and ductility of URM buildings. Clay bricks and eco-friendly fly-ash bricks were used for the construction of the building models. Brick sizes were reduced to half so that the scale-down building model can be constructed for testing. The building models were tested in a uni-directional shaking table using swept sine motions. The experimental investigation was categorized in three phases. In the first phase, the effect of diaphragm action on seismic behaviour of masonry building was investigated by providing the flat reinforced concrete slab and pitched timber truss as a roof on top of the building. The second phase focused on the enhancement of the seismic behaviour of the URM wall by strengthening with two cost-effective materials, such as polypropylene (PP) band and steel wire mesh (WM). In the third phase, cracked (damaged) URM walls were repaired and retrofitted with wire mesh. It was observed that both the strengthening materials were effective in improving the ductility of the URM buildings.

In-plane strength and stiffness of AAC floor without concrete topping in buildings with AAC masonry infill walls - experimental tests and numerical analyses

The diaphragm action of floors strongly influences the local and global seismic response of a masonry building. The American (ASCE 7-16) and European (EC8) Codes provide few and contrasting indications to classify the floor as 'rigid' or 'flexible'. Moreover, there is limited experience regarding the in-plane behaviour of diaphragms made of aerated autoclaved concrete (AAC) panels, and no specific regulations are available for AAC floors. The assessment of in-plane strength and stiffness of AAC floors without a concrete topping is still an open topic. In this work, in-plane diagonal compression tests on AAC precast panels without a collaborating slab are performed to evaluate the behaviour of AAC floors. Panels having a different thickness and depth of the shear key were considered for testing. The experimental results are then applied to two case study buildings to verify through numerical analyses if they behave as 'rigid' or 'flexible'. Numerical results showed an almost 'rigid' behaviour in terms of stiffness, but the in-plane strength is not always assured in conditions of marked irregularities of the building and high seismic-prone areas.

In-plane strength and stiffness of AAC floor without concrete topping in buildings with AAC masonry infill walls - experimental tests and numerical analyses

The diaphragm action of floors strongly influences the local and global seismic response of a masonry building. The American (ASCE 7-16) and European (EC8) Codes provide few and contrasting indications to classify the floor as 'rigid' or 'flexible'. Moreover, there is limited experience regarding the in-plane behaviour of diaphragms made of aerated autoclaved concrete (AAC) panels, and no specific regulations are available for AAC floors. The assessment of in-plane strength and stiffness of AAC floors without a concrete topping is still an open topic. In this work, in-plane diagonal compression tests on AAC precast panels without a collaborating slab are performed to evaluate the behaviour of AAC floors. Panels having a different thickness and depth of the shear key were considered for testing. The experimental results are then applied to two case study buildings to verify through numerical analyses if they behave as 'rigid' or 'flexible'. Numerical results showed an almost 'rigid' behaviour in terms of stiffness, but the in-plane strength is not always assured in conditions of marked irregularities of the building and high seismic-prone areas.

Direct Displacement Based Design of Reinforced Concrete Elevated Water Tanks Frame Staging

Elevated water tanks supported by the reinforced concrete (RC) Staging are classified as inverted pendulum structures. These are considered as structures of high post-earthquake importance and should remain functional after the seismic events. National codes of various countries recommend Force-Based Design (FBD) procedure for water tank staging, which does not ensure nonlinear performance level for a given hazard. Therefore, it becomes necessary to design these structures with a performance-based design approach like Direct Displacement-Based Design (DDBD). Many design engineers consider that the behavior of frame staging of the elevated water tank is similar to the building's frame and generally adopt the same design principles for both types of structures. However, the seismic behavior of the building frame is significantly different from frame staging due to the absence of diaphragm action at the bracing level and concentrated mass at the top level only. Therefore, it may not be rational to utilize the same DDBD procedure of the building's frame for the design of frame staging of the elevated water tanks. The present study proposes some modification in existing DDBD procedure (used for the design of frame building) based on the nonlinear time history analysis of twenty meters high RC frame staging with four different configurations. The modifications are proposed in terms of inelastic displacement profile, design displacement, effective height, and effective mass calculation. Further, the performance of the same RC frame staging designed using the proposed DDBD procedure has been assessed using nonlinear static and dynamic analyses to verify the suitability of proposed modifications.

Practical assessment of the seismic behavior of a confined masonry system

Seismic assessment of the failure mechanisms of masonry buildings can become an onerous task in light of the vast range of typological and structural characteristics of masonry constructions. Ranging from unreinforced masonry old structures that date anywhere from the 19th and early 20th Century, up to contemporary buildings constructed according to modern standards, seismic assessment of masonry buildings challenges the state of the art well beyond the familiar procedures used for Reinforced Concrete and Steel frame structures due to the frequent lack of diaphragm action, their distributed stiffness and mass in the vertical rather than the horizontal elements and the intense brittleness of the material. To facilitate practitioners in assessing the load bearing capacity of existing masonry buildings a practical evaluation procedure was recently introduced by the authors. The procedure allows the determination of the envelope of developed deformations and the tendency for deformation and damage localization throughout the examined building for a given design earthquake scenario, which is then compared with drift capacities of the structural members associated with predefined performance limits. In this paper the assessment procedure is presented through application to two layouts of confined masonry houses, representing many similar structures on the Ionian Island of Cephalonia, Greece, which survived with practically no damage the January 24, 2014 and the February 03, 2014 near-field strong earthquakes of magnitude 6.1 and 6.0 that occurred in the island; these structures were relief-homes made in 1953 under a state of emergency after complete devastation of the island during the 1952 earthquakes of similar magnitude and origin as the 2014 events.

Progressive collapse analysis and structural robustness of steel-framed modular buildings

This paper investigated the structural robustness of steel-framed modular buildings based on the alternative load path method using LS-DYNA. The structural responses of a reference structure were first simulated to understand typical building motion, load redistribution mechanisms and failure modes after removal of a base corner module. Based on the reference scenario, a comprehensive parametric study was then carried out to investigate the effects of structural configuration (number of modules of each floor), module posts (wall thickness and number of supporting posts) and other features (inclusion of floor slab, longitudinal wall bracing, connection stiffness and connection capacity) on the structural responses of steel modular buildings. It was found that the collapse resistance of steel modular buildings could be improved with an increase in the number of modules per floor, the number and capacity of supporting posts, higher rotational stiffness and capacity of inter-module connections, and the use of longitudinal wall bracing. Consideration of floor slabs provided a more realistic description of collapse mechanisms, due to the slab-related contact interaction and diaphragm action. Also, the structure was more vulnerable to the removal of modules (or posts) near the end corner of a building.

Research on Self-Drilling Screwed Lap Connections in Steel Diaphragms and the Design Models

Abstract In this paper, the results of a research on thin-plate single-lap connections are presented. Such type of connections is popular in steel roofs made of trapezoidal plates and other thin-walled elements. In case of a building safety it is necessary to ensure that materials with proper durability and ductility are used. Connections are one of the most important components in such structures, particularly when in-plane strength of a roof is taken into account. So far, in many existing regulations, only general calculations of such connections are conducted. However recently, discrete and computational methods can be used to build new, expanded mathematical design models, such as those presented here. Such models could be useful in an advanced design where a static analysis is combined with the safety assessment of the connections in a structural system. This is difficult when sheeting is utilized as a structural in-plane shear diaphragm. These require to take into consideration the important interactions of structure with covering and covering with another covering elements. The research is an effect of authors works on practical design approaches. Such methods can be effectively used for structural designs of buildings where the stressed skin diaphragm action is involved. Finally, practical input values about connections can be acquired from the presented data.

Interventions to Structural System of Masonry Buildings and their Effects to their Seismic Response

Background: Preservation of listed buildings, depending on the importance of each one, requires the conservation of the whole structure or of only the external walls, often called shell of the building, or even only of the façade. In the latter cases, although the new structure is studied to undergo the applied loads according to the codes in force, less research is made to study the response of the remaining structure under seismic loads. Objective: The response of unreinforced masonry (URM) structures with alterations of the original load bearing system to strong ground motions is studied in the present paper. Commonly used radical interventions comprise the addition of a steel or reinforced concrete frame in the interior of the structure after removal of interior load bearing or/and dividing walls. The embedded substructure is designed to support the functional loads of the building and commensurate seismic design forces associated with its mass. In this setting, perimeter walls are relieved of any bearing action apart from resisting the state of stress associated with their self-weight. An important design decision is the extent of contact and interaction that is allowed to occur between the perimeter URM walls and the interior structural system; both options present advantages and disadvantages. Methods: The effect that this design option has on the seismic response of the composite system is studied in this paper using linear elastic finite element analysis. The effect of each intervention is estimated by comparing the principal tensile stresses (pts) developed on the walls before and after each intervention as well as the percentage of the wall areas in elevation where the pts are higher than tensile strength of masonry. Results: It is found that connection of the frame to the masonry walls at several points around the floor and roof perimeters creates a diaphragm action that effectively reduces the out-of-plane bending of the self-standing perimeter URM walls without excessive local stress intensities and increases the shear strength of the building. Lack of contact between the old and new load bearing elements leads to higher intensity stresses due to bending and only the addition of a reinforced concrete tie belt at the top of the walls may mitigate serious damage. Conclusions: The cooperation of the Moment Resisting Frames, irrespective of the material of the frame (reinforced concrete or structural steel) and the walls by connecting the perimeter structural walls with it at floor and roof levels, is more efficient to the stress state of the walls transforming the critical out-of-plane bending of later to shear one, preventing them from out-of-plane collapse.

The Effects on the Bracing Stiffness of Timber Structures of the Stiffness of Its Members

The design of slender structures is often associated with a number of assumptions made by engineers in checking on the stability of the structure. Not seldom, these assumptions are rather uncertain. In the present paper the effects of the stiffness of different members on the bracing stiffness of timber structures is studied. Both full-scale laboratory testing and FE-modelling are employed here in the investigation. In particular, two different bracing approaches are analysed, those of (1) cross bracing (wind trusses) and (2) diaphragm action (through use of steel sheeting) in the plane of the roof. In addition, the effects of the connections and the number of fasteners used in the structure are evaluated. The stiffness of the connections is obtained by means of an FE-updating approach, i.e. that the relevant parts included in the FE-model are calibrated to ensure that the FE-results match the laboratory results. The findings obtained indicated, (1) that the connections can have a significant effect on the stiffness of the bracing systems, (2) that the cross bracings close to the mid-span of the structure are less effective than those close to the supports, (3) that the lateral stiffness obtained using a diaphragm approach is closely related to the number of fasteners between the steel sheet and the timber parts in the roof that are employed, and (4) that the two different bracing approaches used provide about the same lateral stiffness of the roof. Finally, it should be emphasized that FE-models can markedly overestimate the stiffness of timber structures. If the connections are not modelled accurately, the engineers involved are advised to seek safe sided assumptions regarding them.

Investigating the in-plane flexibility of steel-deck composite floors in steel structures

PurposeIt is common practice in structural engineering to assume floor diaphragms infinitely stiff in their own plane. But, most of the code provisions lack clarity and unity in categorising floor diaphragms and discussing their behaviour based on the seismic response of the structures. Besides, although many of these code provisions have presented simple techniques and formulations for determining the level of flexibility in floor diaphragms, the implementation of these techniques on more complex floor systems such as the steel-deck composite floors is still under question. The paper aims to discuss these issues.Design/methodology/approachIn this study, an equivalent concrete floor is employed as a representative of in-plane diaphragm action of steel-deck composite floor, using simple modelling techniques in SAP2000 and the results are validated by complex structural models developed in ABAQUS. Afterwards, the equivalent floor is inserted to 3, 5 and 7 storey steel structures with 2, 3 and 5 plan aspect ratios in two categories of structures with rigid diaphragms and analogous structures with flexible diaphragms and the responses are compared to each other.FindingsThe results show that the proposed technique is an effective method for evaluating the diaphragm action of steel-deck composite floors. Additionally, it is concluded that, the boundary values of plan aspect ratio equal to 3 and λ coefficient equal to 0.5 in steel-deck composite floors, mentioned in code provisions for categorising diaphragms, are not always conservative and need to be scrutinised.Originality/valueThe proposed methodology provides simple framework for assessing the effects of in-plane flexibility of steel-deck composite on seismic response of steel structures.

Efficacy of roof-to-beam mechanical connections on the diaphragm behaviour of precast decks with spaced roof elements

The diaphragm action of slab/roof decks ensures the collaboration of different parts of the lateral load resisting system of a building. In reinforced concrete precast buildings for industrial/commercial halls, not seldom the deck is not provided with a cast-in-situ topping: this results into diaphragm action to rely upon the floor mechanical connections alone. In this study, the efficacy of three different typical floor-beam connections, namely hot-rolled angle brackets, cold-formed angle brackets and dowel bars, on the diaphragm action of the deck has been investigated. To this purpose, simplified macroscopic “behaviour models” have been proposed, based on the results of monotonic and cyclic tests carried out within the framework of the research project Safecast (FP7-SME-2007-2; GA 218417/2009). A numerical model of a dry-assembled precast structure with mechanical floor-to-beam connections has been checked against the results of cyclic and pseudo-dynamic tests carried out on a full-scale prototype within the framework of the Precast Structures EC8 project (GA G6RD-CT-2002-70002). Non-linear dynamic analyses have then been performed to investigate the diaphragm action effectiveness of the three different technological solutions to connect slab and beams considering a seismic action orthogonal to the roof elements. Different stiffness distributions of the lateral load resisting system have been considered, investigating the possible bracing effect induced by an integrated connection system of the external cladding panels. A simplified “design-wise” analytical interpretation of the phenomenon is also formulated and checked against the numerical results.

Evaluation of diaphragm conditions in AAC floor structures with RC beams

Diaphragm action in floor structures is an important aspect that affects both local behaviors of individual members and consequently, the global response of a structure. The diaphragm action of a built structure, therefore needs to be compatible with the assumed diaphragm condition in the design phase to prevent unpredicted overloading of load bearing members in a seismic action. Autoclaved aerated concrete (AAC) is a cost-effective, lightweight and energy efficient material, and its usage as a construction material has rapidly increased in recent decades. However, there is a limited experience regarding the in-plane behavior of the floor structures made of AAC panels in terms of diaphragm action. In this paper, the in-plane response of AAC floors is experimentally investigated and the floor performance of a typical building is analytically investigated according to ASCE 7-16 (ASCE/SEI in Minimum design loads for buildings and other structures, The American Society of Civil Engineers, Reston, 2016). Full-scale experiments carried out through loading AAC floors in lateral directions to the panels, either parallel or perpendicular, provided important information about the damage progress and overall performance of such floors. A number of finite element modeling techniques that are generally used for modeling of AAC floors were examined and then validated through comparisons with test results. Finally, the diaphragm condition of a three-story building made of AAC walls and floor panels was assessed. The results indicated that the AAC floors in the examined building can be idealized as rigid diaphragms according to ASCE 7-16.

Experimental full-scale tests on steel portal frames for development of diaphragm action – Part I experimental results

Previous studies on stressed skin effect of industrial steel buildings showed discrepancies between the ECCS formulae and experimental results. To clarify the discrepancies full-scale experimental test program was planned and executed by the Budapest University of Technology and Economics, Department of Structural Engineering. The aims of the full-scale tests were to refine the stressed skin design method and to adjust it to the nonstandard cladding structural system applied by an industrial partner. During execution of the full-scale experiments the shear flexibility of those industrially applied nonstandard diaphragms were examined, where the application of seam fasteners were rejected. Next to the building section a loading frame was built, so that tension and compression force could be applied to each frame, in order to examine the in-plane shear flexibility of the whole nonstandard diaphragm assembly, including the shear flexibility of the portal frame. In the test series four purlin and two trapezoidal sheeting height configurations were combined in more than 100 tests. This paper, denoted as Part I shows the test setup and introduces the results derived from the ECCS formulae, underlining the importance of extending the applicability of the current design formulae to nonstandard cases, which are often applied in industrial practice all over Europe. A companion paper (Part II) presents the comparative results between the various cladding configurations, also the main conclusions regarding the stiffening effect of the applied diaphragm configurations, and reports the effect of change in section size to shear flexibility. Besides this in Part II the effect of different structural components in regards to shear flexibility is underlined.

Experimental full-scale tests on steel portal frames for development of diaphragm action – Part II Effect of structural components on shear flexibility

The Part II of this two-part paper evaluates the results of the experimental test series introduced in Part I. This research aimed to examine the major influencing parameters of stressed skin effect in industrially applied, nonstandard diaphragm configurations. As no international study was executed in state of art, in order to study the role of different variables to shear flexibility, a full-scale test series was executed at the Budapest University of Technology and Economics, Structural Engineering Department. In Part I the experimental test arrangement and shear flexibility results are introduced in comparison with the results derived from the ECCS formulae. This paper, denoted as Part II details the evaluation of full-scale test results by underlining conclusions regarding the effect of change in section size of structural components and the number of fixings, and the effect of variation in structural arrangements. The results of this investigation shows that in nonstandard cases the stiffening effect of diaphragms are comparable to the stiffening effect of bracing.

Seismic performance of precast concrete structures with energy dissipating cladding panel connection systems

The cladding‐structure interaction of precast concrete frame systems under seismic action has not been properly addressed in the past, as shown by several failures occurred under recent earthquakes in Southern Europe, which point out the need of a revision of the current design practice and technology. Dissipative systems of connections are proposed to this purpose within a general framework for seismic design of precast structures with cladding panels. The proposed connection systems consist of friction‐based or plasticity‐based devices interposed in between adjacent cladding panels or between the panels and the resisting frame to control the level of transferred forces and limit the displacements of the structure. Monotonic and cyclic experimental tests are carried out on both single connection devices and structural sub‐assemblies of two panels. Furthermore, cyclic and pseudo‐dynamic tests on a full‐scale prototype of precast structure with cladding panels are performed. The influence on the structural response of silicone sealant is also investigated through experimental testing. The effectiveness of the tested dissipative connections of the cladding panels in enhancing the seismic performance of precast structures is demonstrated by means of nonlinear dynamic analyses considering the influence of the roof diaphragm action. Design guidelines are finally provided for both single connectors and panel structural assemblies based on equilibrium and capacity design criteria.

Experimental and Safety Evaluation of Cold-Formed Steel Standing-Seam Metal Roof Panels

Failure of metal roof is the most commonly observed damage in cyclones. Significant numbers of metal roof coverings, corners, and eaves are damaged. International codes of practice specify the procedure for the calculation of structural capacity of purlins supporting standing-seam metal roof (SSMR) systems, but they do not specify the procedure to design the panel–purlin connection system, integrated by a clip called a halter. The panel profiles and fastening techniques adopted worldwide are so diverse that the strength of panel–purlin connection and the lateral restraint on purlin by diaphragm action cannot be generalized. However, the type of standing-seam system presented in this paper, viz., the clip lock system, is prevalent in many countries with uniformity in halter dimensions and seam heights. The details of an experimental investigation on prototype cold-formed steel (CFS) standing-seam clip lock system tested under wind uplift in a vacuum chamber are presented here. A vacuum chamber was fabricated specially for this purpose, as per standards. The behavior and failure modes of rigid purlin-panel system were studied. Experimental data on the uplift behavior of SSMR were gathered. This data were converted to design parameters through statistical evaluation. Three limit states of panel-purlin interaction failure were studied and a procedure for the integral design of SSMR halter-rigid purlin systems was developed, guided by the experimental results. On the design effect side, four wind-pressure cases, along with cyclonic wind pressure, were considered. The applicability of the experimental results to practical designs was quantified by a reliability-based analysis. Based on the values of reliability indices, the zones of failure were identified, and a rational design of variable halter length was proposed. The halter length could be adjusted as per the target reliability, leading to the concept of SSMR roof system with a uniform safety.

Proposals for seismic retrofitting of timber roofs to enhance their in-plane stiffness and diaphragm action at historical masonry buildings in Cairo

Abstract The in-plane stiffness of flat roofs plays crucial role in the structural stability and safety of historical load bearing masonry buildings under lateral hazardous loads. For decades, many restorers of historical buildings used to provide the original timber roofs with rigid diaphragms action using modern engineering systems; such as building reinforced concrete (R.C.) thin slabs. The present research studies analytically the installation of simple and robust timber bracing system above timber boards and under flooring layers of timber flat roofs; to improve the seismic behavior and stability of their historical load bearing masonry buildings in Cairo. The study will evaluate among various alternatives of bracing systems using numerical modelling techniques of computer software that applies Finite Element (F.E.) method. The research applies the numerical investigation to one of archaeological buildings in Cairo from Ottoman era, which is the “Sabil” of “Khusraw Pasha” (1535 A.D./942 A.H.). The timber x-bracing system provides remarkable results relative to rigid diaphragm and steel bracing for seismic retrofitting of historical timber roofs.

07.37: Development in calculation of stressed skin effect upon experimental and numerical research results

ABSTRACTThe opportunities of improvement in stressed skin design formulae in the European Convention for Constructional Steelwork (ECCS) publication are reviewed in this paper.Stressed skin effect is the diaphragm action provided by the in‐plane stiffness of a diaphragm assembly. The diaphragm is composed of panel assemblies transmitting in‐plane forces to the main frames, providing considerable stabilizing effect to the building. The stiffening effect of diaphragm assemblies depends on their components: type of supporting frame, type of sheeting, number of fixings and the connection between sheeting and purlins.This paper first discusses the results of an experimental analysis carried out in the Structural Laboratory of the Budapest University of Technology and Economics. The experimental programme aimed to study the stiffness of various diaphragm configurations. Based on the results, the principal influencing parameters are identified. The results confirm that the eccentricity of the connected members – that is out of consideration in current Eurocode provisions – play significant role in the stiffness, and thus it should be considered in design for stressed skin effect. The experimental results also served as a basis for numerical model development and calibration. The verified FE model is capable for numerical simulation of any kind of diaphragm assembly. The paper introduces the results of a parametric study aiming to extend the real experimental results by further virtual experiments.Based on the experimental and numerical results, modifications are proposed to the current Eurocode provisions, in order to capture all influencing parameters and thus to extend the applicability of the standard design model for “non‐standard” configurations that are commonly installed in practice as well.

03.15: Experimental tests and model study on self‐drilling screws connections subjected to shear

ABSTRACTResearch on shear resistance of the steel sheeting plates with thickness from 0,50 to 1,50 mm connected by self‐drilling screws is undertaken and presented in this paper. One screw type with one diameter has been used. This kind of the single lap fastening is commonly used in a steel sheeting. Experimental and theoretical data about a connections slip and shear stiffness is a one of most important issue in case of a stressed skin diaphragm action problems. At the present practice the linear model of connections is effectively used however for more advanced analyses, the non‐linear models have to be taken into consideration. These are necessary in case of the advanced design and implementation of the stressed skin action in the steel structures covered by the corrugated metal sheeting. Such a model study is presented herein which intend to investigate the general connection behaviour where the main selected variable is the plate thickness. The test are performed according to the current standards EN 1990 and ECCS handbooks. It leads to a statistical evaluation of proposed functions for the design slip of fasteners and its limits. The theoretical basis of experimental tests under the shear load is presented.