Two-dimensional Frame Structure Research Articles

Fail-safe optimization of tubular frame structures under stress and eigenfrequency requirements

In conventional fail-safe optimization of frame structures the damage is usually modelled as complete removal of one or more members. We propose and incorporate two additional types of damage models into the fail-safe design problem. The first describes thickness degradation caused e.g. by corrosion. The second describes severe local damage by removal of a part of a member that causes a gap and free ends in the member. The latter damage model can cause undesirable local vibration modes. By combining the two damage models, local thickness degradation in a part of a member can be modelled. The considered design problem minimizes structural mass and includes local stress constraints and limits on eigenfrequencies. Besides the new damage models, a working-set algorithm is applied on the fail-safe optimization problem to reduce the computational cost. Numerical experiments on two-dimensional frame structures illustrate that the working-set algorithm can effectively handle the relatively large number of constraints and damage scenarios in fail-safe optimization.

Software Engineering Development of Finite Element Method Programming Applications in 2D Frame Structures Using Python Programs

The application of the Finite Element Method as one of the numerical methods to solve various engineering problems is of course inseparable from the development of computers with various other related fields such as Computer Aided Design (CAD) and Computer Aided Engineering (CAE) which continuously becomes a concentration of interest in the engineering field. Element analysis has so far been in great demand by various industries due to its reliability and speed in terms of optimization in the world of design and analysis. There are many finite element software such as Abaqus, Nastran, Ansys, CosmosWork, LS-Dyna, Pro-Mecanica, SAP2000. However, the application is paid at a relatively high cost and has quite strict licensing rules, of course this is an obstacle for students at the University of Riau who want to use it. From these problems the author is interested in developing a programming application that can be an alternative to analyzing a structure. The solution that the author can propose is to develop an application using the python programming language to analyze a two-dimensional (2D) frame structure that is under load and is in an elastic condition. From the results of the research that has been carried out, the simulation results of the frame A model obtained data on the 2nd frame model of frame A, the horizontal displacement of -0.06098 m, the vertical displacement of -0.00002857 m, and the angular displacement of 0.00762 rad. These results are compared with manual solutions, analytical solutions, and previous research, it can be concluded that the results of calculations in the developed application show values that are close to that comparison, where the percentage error is not more than 3%, with the highest percentage difference of 2.5%.

Optimal design of planar steel frame structures utilizing meta-heuristic optimization algorithms

Meta-heuristic algorithms are applied in optimization problems in a variety of fields, including engineering, economics, and computer science. In this paper, seven population-based meta-heuristic algorithms are employed for size optimization of two-dimensional steel frame structures. These algorithms consist of the Artificial Bee Colony algorithm, Big Bang-Big Crunch algorithm, Cyclical Parthenogenesis Algorithm, Cuckoo Search algorithm, Thermal Exchange Optimization algorithm, Teaching-Learning-Based Optimization algorithm, and Water Evaporation Optimization algorithm. Optimization aims to minimize the weight of rigid-jointed steel frame structures while satisfying some constraints on displacement and stress limits. The design is based on the requirements of the AISC Load and Resistance Factor Design (LRFD). The capability and robustness of the algorithms are investigated through three well-known steel frame benchmarks.

Band gap characteristics of flexural wave of two-dimensional periodic frame structure composed of locally resonant composite beam

Abstract In this paper, single material beams as the basic structural members in the traditional periodic frame structure were extended to the ones of multi-material composite beam with locally resonant (LR) unit. Based on the spectral element method and the topological characteristics of structure, an assembly method of the stiffness matrix for virtual full component model is presented. This method can be applied not only to the periodic structures, but also to the aperiodic structures, because the whole stiffness matrix of the structure is assembled by its topological information. The effects of the rest design parameters on the band gap behavior of two-dimension (2D) periodic frame structure were studied when the lattice constant was fixed. The results show that the Bragg band gaps can be adjusted by changing the lengths of structural members and the length ratio of the subunit A to the structural members. The results also show that the LR band gaps can be adjusted by adding LR units with different parameters into different members. The results in this work enrich and expand the modulatory pathway of the band gaps of periodic frame structure, and provide a modified approach to the design and correction of the passive vibration suppression system.

A dual adaptive filtering approach for nonlinear finite element model updating accounting for modeling uncertainty

Abstract This paper proposes a novel approach to deal with modeling uncertainty when updating mechanics-based nonlinear finite element (FE) models. In this framework, a dual adaptive filtering approach is adopted, where the Unscented Kalman filter (UKF) is used to estimate the unknown parameters of the nonlinear FE model and a linear Kalman filter (KF) is employed to estimate the diagonal terms of the covariance matrix of the simulation error vector based on a covariance-matching technique. Numerically simulated response data of a two-dimensional three-story three-bay steel frame structure with eight unknown material model parameters subjected to unidirectional horizontal seismic excitation is used to illustrate and validate the proposed methodology. Geometry, inertia properties, gravity loads, and damping properties are considered as sources of modeling uncertainty and different levels and combinations of them are analyzed. The results of the validation studies show that the proposed approach significantly outperforms the parameter-only estimation approach widely investigated and used in the literature. Thus, a more robust and comprehensive identification of structural damage is achieved when using the proposed approach. A different input motion is then considered to verify the prediction capabilities of the proposed methodology by using the FE model updated by the parameter estimation results obtained.

LTE commsense for object detection in indoor environments

In this work, we describe a new method of using long-term evolution (LTE) telecommunication infrastructure to sense environmental changes. We call it LTE communication-based sensing (Com-mSense). It can be used in various environment-sensing tasks, e.g., sea level monitoring, security of large unmanned landscapes, snow avalanche monitoring, and activity detection inside forests. The main concept of this technology is to focus on the known signal embedded in the data frames. It compares the received signal with the expected reference signal to estimate the change in the environment. LTE telecommunication infrastructure is used for this environment-sensing task because of its wide coverage. In addition, LTE uses a two-dimensional (2D) frame structure of orthogonal frequency division multiplexing (OFDM) and multiple input and multiple output (MIMO), which may yield better performance compared to previous communication standards. This procedure of extracting channel characteristics using commensal radar principles does not affect the existing telecommunication system, because it is a receive-only system. After the channel characteristics are estimated, they can be used to obtain phenomenological knowledge of the environment using an application-specific instrumentation (ASIN) framework. The capability analysis of this scheme is presented in this article, first in simulation and then using field-collected data captured with the help of a software-defined radio (SDR) platform.

Republished Paper. Multiple damage detection and localization in beam-like and complex structures using co-ordinate modal assurance criterion combined with firefly and genetic algorithms

Damage detection and localization in civil engineering constructions using dynamic analysis has become an important topic in recent years. This paper presents a methodology based on non-destructive detection, localization and quantification of multiple damages in simple and continuous beams, and a more complex structure, namely two-dimensional frame structure. The proposed methodology makes used of Firefly Algorithm and Genetic Algorithm as optimization tools and the Coordinate Modal Assurance Criterion as an objective function. The results show that the proposed combination of Coordinate Modal Assurance Criterion and Firefly Algorithm or Genetic Algorithm can be easily used to identify multiple local structural damages in complex structures. However, the convergence rate becomes slower for the case of multiple damages compared to the case of single damage. The effect of noise on the algorithm is further investigated. It is found that the proposed technique is able to detect the damage location and its severity with high accuracy in the presence of noise, although the convergence rate became slower than in the case when no noise is present. It is also found that the convergence rate of Firefly Algorithm is much faster than that of Genetic Algorithm.

Modeling Dynamics of a Building Using a Portal Frame Approach

Building service equipment, such as ventilators, air conditioners, and cooling tower are structure-borne sources that are capable of injecting vibration input power to the building structure. The vibration waves propagate through the building elements and can result in audible low frequency noise. This paper proposes the development of an analytical model of the dynamics of a building using a two-dimensional portal frame structure consisting of beam and truss elements. The structural response due to an injected force from a structure-borne source is studied and is compared with a three-dimensional model from the Finite Element Method. It is shown that the vibration pattern from the two-dimensional result follows the pattern of that from the three-dimensional model for vertical vibration. The two-dimensional model can thus be used for a simple modelling to understand the behavior of the building vibration.

Fiber-Section Model with an Exact Shear Strain Profile for Two-Dimensional RC Frame Structures

AbstractA fiber-section model for nonlinear analysis of shear-critical reinforced concrete frames is developed. The model incorporates a new procedure for the computation of an exact shear strain p...

Experimental study on dynamic responses of reinforced concrete frames under sudden column removal applying concentrated loading

This paper focuses on structural behaviour of storeys above the targeted column that is suddenly lost due to accidental/terrorist events. The pertinent question is whether these storeys will remain stable, or the ensuing dynamic motion will cause them to fail during the free-fall stage. It is assumed that the two-dimensional frame structure above the targeted column is in pristine state. Previous quasi-static studies on reinforced concrete beam-column structures under missing column scenario have highlighted the potential of catenary action on providing alternate load paths to prevent catastrophic collapse. However, corresponding dynamic tests, either did not share the same loading configuration with the static tests, or did not have sufficient headroom and the specimen hit the ground before catenary action could be fully mobilised. On this paper, a series of dynamic tests was carried out for two-dimensional reinforced concrete beam-column frames simulating the sudden removal of a supporting column via a quick-release device. The specimens were loaded and hung by a mechanism which could be released to effect free vibration. Development of catenary action, which has not yet been confirmed in any previous dynamic tests, was well captured. The study also showed the influence of inertial and strain rate effects on structural response. Most importantly, the dynamic tests applied the same method of concentrated loading at the middle joint as the previous quasi-static tests conducted on similar specimens. As a result, comparisons could be made on damage patterns and failure modes between the dynamic tests and the static tests. Compared to static environment, the dynamic tests only took a few seconds and their behaviours are closer to the actual behaviour of the storeys that undergo free-fall acceleration.

Multiple damage detection and localization in beam-like and complex structures using co-ordinate modal assurance criterion combined with firefly and genetic algorithms

Damage detection and localization in civil engineering constructions using dynamic analysis has become an important topic in recent years. This paper presents a methodology based on non-destructive detection, localization and quantification of multiple damages in simple and continuous beams, and a more complex structure, namely two-dimensional frame structure. The proposed methodology makes used of Firefly Algorithm and Genetic Algorithm as optimization tools and the Coordinate Modal Assurance Criterion as an objective function. The results show that the proposed combination of Coordinate Modal Assurance Criterion and Firefly Algorithm or Genetic Algorithm can be easily used to identify multiple local structural damages in complex structures. However, the convergence rate becomes slower for the case of multiple damages compared to the case of single damage. The effect of noise on the algorithm is further investigated. It is found that the proposed technique is able to detect the damage location and its severity with high accuracy in the presence of noise, although the convergence rate became slower than in the case when no noise is present. It is also found that the convergence rate of Firefly Algorithm is much faster than that of Genetic Algorithm.

Study of geometric non-linear instability of 2D frame structures

AbstractIn this work, we deal with the geometric instability problem of the two-dimensional (2D) elastic frame structures undergoing large overall motion. The geometrically exact beam model with total Lagrangian formulation is used to obtain the solution to non-linear instability problems with large pre-buckling displacements. We propose, in particular, a study of dynamic analysis that can deal with instability problems of this kind with no need for any load decrease. The dynamics approach provides a more realistic post-buckling behaviour for the case of snap-through or snap-back. The material damping is necessary when a classical time integration scheme like Newmark is used. The principal novelty in this work is to consider non-linear damping to avoid the vibration around the equilibrium point when a classical scheme as Newark is used. The efficiency of the damping model and methodology analysis are illustrated by a number of numerical simulations.

Dynamic characterization of full-scale structures made with recycled coarse aggregates

The incorporation of recycled aggregates produced from concrete waste is an option that could reduce the consumption of natural resources and landfill disposal, with significant environmental gains. Several investigations have been conducted to study the viability of this use of concrete waste, with a focus on the material, mechanical and durability related behaviour of recycled aggregates concrete. The structural behaviour has not been properly studied to date, despite some investigations already performed on two-dimensional scaled-down frame structures and on concrete elements, like beams and column–beam joints. To encourage the use of recycled aggregates concrete, the authors conducted experiments on four full-scale recycled aggregates concrete structures with various recycled aggregates incorporation ratios. Here, the dynamic characterization tests made on the structures are described and analysed. The concrete Young's modulus of finite elements models of the test-structures was calibrated with data from the tests, namely the natural frequencies associated with each modal shape. It was proven that the pattern of response of the different structures was the same and that the aggregates used had a relatively small influence on the Young's modulus. One of the concrete mixes included a superplasticizer and the use of this admixture resulted in a concrete structure with higher stiffness than all the other mixes, including a reference mix with no recycled aggregates. To the authors' best knowledge, this is the first study regarding the dynamic behaviour of full-scale recycled aggregates concrete structures and the dynamic properties of recycled aggregates concrete.

Preliminary ranking of alternative scalar and vector intensity measures of ground shaking

In Performance-Based Earthquake Engineering, seismic demand in structures is predicted by building probabilistic seismic demand models that link measures of earthquake intensity (IMs) to measures of structural demand. Investigations are carried out herein for evaluating the predictive capability of a wide range of commonly-used scalar and vector-valued IMs for different peak-related demand parameters. To accomplish this goal, both efficiency and sufficiency of the candidate IMs are taken into account. The latter is evaluated with the recently-proposed “relative sufficiency measure”. This measure, which is derived based on information theory concepts, quantifies the amount of information gained (on average) by an IM relative to another about the demand parameter of interest. Evaluation of the IMs, herein, uses two sets of ground motions consisting of ordinary and pulse-like near-fault records. Two-dimensional RC frame structures, both fixed and isolated at the base, are selected. The most suitable IMs for predicting the considered different demand parameters and types of structure are identified in terms of both efficiency and sufficiency. The use of these most informative IMs is suggested to build improved probabilistic demand models.

Damage identification of a frame structure model based on the response variation depending on additional mass

The structural health evaluation is performed by comparing the responses between the undamaged and damaged states. Because it is impractical to collect the response data at the intact state, it is important to establish the baseline data to be compared at measurement. The measured frequency response functions (FRFs) in the neighborhood of the first resonance frequency are transformed to the proper orthogonal mode (POM) corresponding to the first proper orthogonal value (POV). The POM data set at the first measurement on the damage-expected structure is taken as the baseline datum, and it is compared with another set extracted from the structure to attach a small mass on an element. The POM difference between two states is utilized as an index to detect damage. The FRF variation before and after a small mass attachment for the purpose of detecting the damage is investigated. The validity of the proposed method based on POM variation is illustrated in the damage detection of a two-dimensional frame structure model. It is shown that the damage region in the frame structure can be inferred by gradually narrowing from the global structure to the damage-expected element.

Decaying/conserving implicit scheme and non-linear instability analysis of 2D frame structures

In this work we deal with the geometric instability problem of the two-dimensional elastic frame structures undergoing large overall motion. The geometrically exact beam model with total Lagrangian formulation is used to obtain the solution to non-linear instability problems with large pre-buckling displacements. We have proposed, in particular, the use of the conserving and decaying scheme for dynamic analysis that can deal with instability problems of this kind with no need for structural damping, whereas it is necessary when a classical time integration scheme like Newmark is used. This scheme is an extension of time-integration energy conserving scheme presented in Ibrahimbegovic and Mamouri [1], redesigned to introduce desirable properties of controllable energy decay in higher modes, which improve its stability and accuracy. The efficiency of the proposed scheme in non-linear instability is illustrated by a number of numerical simulations.

Hierarchical Structures for a Robustness-Oriented Capacity Design

In this paper, the response of two-dimensional framed structures made of rectangular cells to the sudden removal of columns is studied. A simulation algorithm based on the discrete-element method is employed, where the structural elements are represented by elasto-plastic Euler-Bernoulli beams with elongation-rotation failure threshold. The effect of structural cell slenderness and of topological hierarchy on the dynamic residual strength after damage R1 is investigated. Topologically hierarchical frames have a primary structure made of a few massive elements, while homogeneous frames are made of many thin elements. It is also shown how R1 depends on the activated collapse mechanisms, which are determined by the mechanical hierarchy between beams and columns, i.e., by their relative strength and stiffness. Finally, principles of robustness-oriented capacity design that seem to be in contrast to the conventional antiseismic capacity design are addressed.

Damage Detection Method Based on Element Modal Strain Energy Sensitivity

In this paper, a damage detection method based on an efficient algebraic algorithm of element modal strain energy sensitivity is proposed for detecting damage location and severity. The method adopts a closed form of element modal strain energy sensitivity. The element damage equations have been systematically established and a solution technique incorporated with the singular value decomposition-based regularization algorithm is used to ensure the correct solutions. A number of assumed damage scenarios for numerically simulated beams and two-dimensional frame structure have been used to demonstrate the applicability of proposed method. The noise effect is also presented. It is demonstrated that the proposed method is efficient in a one-step (non-iterative) procedure.

Joint channel estimation and time-frequency synchronization for uplink TDS-OFDMA systems

As one of the key technologies of the Chinese national digital television terrestrial broadcasting (DTTB) standard, time domain synchronous OFDM (TDS-OFDM) is used in the downlink broadcasting transmission scenarios. Based on TDS-OFDM, the uplink multiple access scheme called TDS-OFDMA has been recently proposed. The TDSOFDMA system assumes perfect timing and frequency synchronization, both of which are difficult to be achieved in the uplink transmission where each user's signal is characterized by the user-specific timing and frequency errors. By utilizing the time-domain constant amplitude zero autocorrelation (CAZAC) training sequence and the timespace two-dimensional frame structure, this paper proposes a joint channel estimation and time-frequency synchronization scheme for TDS-OFDMA. The channel estimation has the minimum mean square error (MSE), the timing synchronization is accurate and the frequency synchronization error can reach the Cramer-Rao lower bound (CRLB). The joint algorithm only relies on the time-domain circular correlation, thus low complexity is achieved. Simulation results demonstrate the performance of the proposed joint method under both additive white Gaussian noise (AWGN) and multi-path channels.

Model Conversion Technique for Structural Dynamic Systems

This technical note introduces a novel model conversion technique for structural dynamic systems that is capable of converting a physically realizable, higher-order model (termed the source model) into a completely different, predefined, physically realizable, lower-order model (termed the target model). Upon the complexion of the conversion, the resulting target model preserves or approximates the dynamic characteristics—the chosen structural frequencies and their mode shapes—of the source model. Mathematically, the procedure to implement the model conversion technique is like a model updating approach, which is fundamentally different from that used in traditional model reduction schemes. A numerical example of converting a five-story two-dimensional frame structure model into a five-story classical/generalized one-dimensional shear-building model is demonstrated.