Structural evaluation of a 1971 reinforced concrete building with limited documentation: a hybrid experimental-numerical approach

PurposeMinarets, which were constructed from different types of materials, are slender and tall structures. Minarets could vary in terms of the construction technique, geometry and material. The seismic vulnerability and dynamic behavior of minarets could be different because of these reasons. Full-scale evaluation of minarets includes both experimental and numerical investigations. Experimental methods provide knowledge on the in situ conditions. The structural analysis and performance evaluation can be performed by using numerical methods. In this paper, full-scale structural evaluation of the Trabzon Fatih Mosque Minaret was presented by using experimental and numerical methods.Design/methodology/approachFirstly, the finite element (FE) model of the minaret was generated by ANSYS software. Then, experimental measurements were carried out under environmental vibrations with newly developed vibration system. Afterwards, the initial FE model of the minaret was updated by using manual updating method according to the experimental measurement results. For the seismic performance assessment of the historical minaret, the time history and response spectrum analyses were performed on the initial and updated FE models using the acceleration records of 2023 February Kahramanmaras earthquake and TBEC 2018 codes. The results were evaluated comparatively, revealing that the nonlinear analyses produced higher values compared to other methods. Additionally, variations were observed in the updated FE model results compared to the initial FE model. Finally, it was seen that the minaret did not have sufficient strength against Kahramanmaras earthquake load, so it could collapse under such an earthquake.FindingsBy employing model updating method, the average absolute difference was substantially reduced from 9.12% to 2.11%. The maximum displacements increased with the effect of model updating in all analyses. It was also seen that the spectrum analyses results had lower values than the time-history analyses results and the displacement of the updated FE model was found to be approximately 8% greater than that of the initial FE model in the nonlinear analyses. The maximum/minimum principal stresses decreased in the updated model in the linear analyses. Also, it was determined that the equivalent stresses were higher in linear analyses. It was seen that the cracks occurring in the nonlinear analyses were concentrated more intensely at the bottom region, the transition segment and around the balcony of the minaret. The concentration of damage in these regions suggested that special attention was needed to increase structural durability. The drift ratios were calculated as 0.0056 and 0.0076 for the initial and updated FE models in the linear analyses, respectively. The initial FE model remained the CD limit, but the updated model reached the limit in CP. The drift ratios were calculated as 0.0087 and 0.0093 for the initial and updated FE models in the nonlinear analyses. Both the FE models reached the CP limit. It could be concluded that the minaret did not have sufficient strength against Kahramanmaras Earthquake, so it could collapse under such an earthquake. The drift ratios were calculated as 0.0041 and 0.0043 for the initial and updated FE models in the spectrum analyses. Both the FE models remained within the CD limit.Originality/valueThis paper aimed to evaluate effects of FE model updating on the dynamic and seismic behaviors of the historical Fatih Mosque Minaret in Trabzon. Structural behavior of the minaret was investigated using both experimental and numerical methods. For this purpose, 3-D FE model generated with ANSYS software of the minaret was updated according to the ambient vibration test results. Ambient vibration tests were conducted by measurement system, which was developed by our research team. The manual model updating method was utilized to minimize the differences between numerical and experimental results by varying the material properties. The linear–nonlinear time history analyses and response spectrum analyses were carried out to evaluate the seismic performance of the initial and updated FE models using the acceleration records of 2023 February Kahramanmaras Earthquake records and TBEC 2018 codes.

Structural safety assessment of bowstring type RC arch bridges using ambient vibration testing and finite element model calibration

In this paper the initial finite element model (IFEM) of the Jing Yue Yangtze River Highway Bridge was established and achieved the reasonable finished state of the bridge, which was the large-span, unequal height pylons and mixed beam cable-stayed bridge. The three-dimensional IFEM of the bridge accurately reflected its mechanical behavior under the static loading, and the structure physical parameters and stiffness of the IFEM didn’t need updating through the static loading test. The boundary condition parameters of the IFEM were updated through comparing the measured modal results of the dynamic loading test with the modal analysis results of the IFEM. The updated finite element model can truly reflect the dynamic characteristics of the bridge structure, and the model can be used as the benchmark finite element model, which can provide reliable calculation benchmark of the long term status assessment during the service stage.

Lateral resistance capacity of stiffened steel plate shear walls

Predicted results of a finite element model used to develop physical test structures are often found to be not in a good agreement with the experimental results due to the invalid assumptions made in the finite element modelling. This study will focus on improving the correlation level between the finite element model and experimental model of a car trunk lid with the presence of resistance spot welded joints using modal based updating method. The natural frequencies and mode shapes computed from the updated finite element model of the car trunk lid are compared with the corresponding experimental results. HyperWorks and Leuven Measurement System (LMS) test are used for the modelling and modal testing. MSC Nastran SOL200 is used to identify potential updating parameters and to improve the initial finite element model in the light of corresponding experimental results which are obtained from modal testing. The comparison of the results showed that the total error of 58.59 per cent predicted from the initial finite element model of the trunk lid has been successfully reduced to 3.62 per cent. In conclusion, modal based updating has been successfully used to improve the correlation level between the initial finite element model and the physical model of the trunk lid.

Finite element (FE) model of a square cantilevered plate instrumented with a piezoelectric sensor and an actuator is created using Hamilton’s principle. Rotational degrees of freedom (dofs) of the FE model are eliminated using system equivalent reduction expansion process (SEREP). Experimental mode shapes and natural frequencies are extracted from the structure using high speed cameras and digital image correlation (DIC) technique. Initial FE model is updated using experimental mode shapes and natural frequencies by well-known Berman and Nagy approach. Updated FE model thus derived is further reduced to first three modes using orthonormal modal reduction technique. Modal model of the smart plate is then used to derive state space model of the smart plate. Two Kalman observers are constructed: one using initial FE model and other using updated FE model. Active vibration control experiments are conducted on the cantilevered using these two Kalman observers in the control law. It is observed that much better vibration suppression occurs when Kalman observer based on updated FE model is used in the control law. Strategy suggested in this work to implement a typical active vibration control scheme on a structure is simple and yet very effective.

Lateral shear resistance capacities of face-to-face single-staple and one-row vertically aligned multistaple joints in three oriented strandboards (OSB) were investigated and compared. Experimental results from testing single-staple joints indicated that the face strand orientation of OSB materials had no significant effect on their staple holding capacity in resisting lateral shear loads. The OSB-III with a density of 35.19 pounds per cubic foot (pcf; 563 kg/m3) had a significantly higher lateral shear resistance capacity than OSB-II, with a density of 29.12 pcf (466 kg/m3). Results of multistaple joints indicated that there was no significant difference in lateral shear load resistance capacities between OSB-II and OSB-III joints. The lateral shear load resistance capacity of multistaple joints increased significantly as the number of staples increased from two to four in increments of one. Two alternative power equations were suggested to estimate the lateral shear load resistance capacity of face-to-face one-row vertically aligned multistaple joints in OSB. One equation requires knowing the lateral shear resistance load of single-staple joints in an OSB material, and the other one requires knowing the density of the OSB material constructing the joints.

Optimal reference sensor positions using output-only vibration test data

This paper presents an approach by combining the genetic algorithm (GA) with simulated annealing (SA) algorithm for enhancing finite element (FE) model updating. The proposed algorithm has been applied to two typical rotor shafts to test the superiority of the technique. It also gives a detailed comparison of the natural frequencies and frequency response functions (FRFs) obtained from experimental modal testing, the initial FE model and FE models updated by GA, SA, and combination of GA and SA (GA–SA). The results concluded that the GA, SA, and GA–SA are powerful optimization techniques which can be successfully applied to FE model updating, but the appropriate choice of the updating parameters and objective function is of great importance in the iterative process. Generally, the natural frequencies and FRFs obtained from FE model updated by GA–SA show the best agreement with experiments than those obtained from the initial FE model and FE models updated by GA and SA independently.

Usually the structure of the initial finite element model can not reflect the actual situation of structure, the finite element model updating is for the initial finite element model of the structure, according to the static and dynamic response of the structure of the measured optimize the model parameters are adjusted, the revised model response is more close to the actual structural response, so as to get a more accurate finite element model. In this paper, the finite element model of the bridge is updated by using the second order incomplete polynomial response surface model. Then determine the sample data, use the least squares method to fit the undetermined coefficients of the second-order incomplete polynomial, and perform the accuracy test. Then the objective function based on frequency is constructed, and the updated optimal design parameters are obtained by quadratic sequence programming. Finally, using the optimal design parameters for modal analysis, it is found that the frequency error has decreased. It is proved that the correction by the response surface method (RSM) can improve the accuracy of the finite element model.

The accuracy of the predicted dynamic behaviour of a structure is highly dependent on the accurate properties used in the analytical model. The predicted results computed from the finite element method used to develop the model are often found not to be in good agreement with the experimental results due to the erroneous assumptions made in the finite element modelling. One way to systematically correct the finite element model is to use model updating methods. The main goal of this study was to systematically improve the predicted dynamic behaviour of a car trunk lid using the modal based updating method. HyperWorks and Leuven Measurement System (LMS) test were used for the finite element modelling and modal testing respectively. In order to evaluate the capability of the modal based updating in improving the finite element model, the natural frequencies and mode shapes computed from the updated finite element model of the trunk lid were compared with the corresponding experimental results. The comparison of the results showed that the total error of 65.48 percent predicted from the initial finite element model of the trunk lid has been successfully reduced to 4.74 percent. In conclusion, modal based updating has been successfully used to reconcile the initial finite element model with the physical model of the trunk lid.

Experimental investigation on lateral resistance capacity enhancement effect of a self-centering shape factor in self-centering pier systems

<p>This study presents the implementation of a sensitivity-based finite element model updating process on a 48.6 m long, multi-span, reinforced concrete railway bridge located in Stange, Norway. Lack of documentation and uncertainties surrounding the boundary conditions combined with unrealistic dynamic response obtained from dynamic analysis using a finite element model based on the design drawings prompted the need for monitoring of the vibrations on the bridge followed by identification of modal properties and development of an updated finite element model which can more accurately represent the as-built structure.</p><p>For this purpose, the railway bridge was instrumented and vibration data from operational conditions was collected. Using the covariance- driven stochastic subspace identification method, the modal properties of the bridge were identified from the recorded vibrations. Comparison of the identified mode shapes with those obtained from the documentation-based initial finite element model showed significant discrepancies depicting the shortcomings of the initial model. A comprehensive sensitivity analysis and iterative finite element model updating was undertaken with a specific focus on the boundary conditions to obtain a FE model that can replicate the observed behaviour. As a result, the correlation between the observed and computed mode shapes were increased to 89% from 61% and the average error in the first four natural frequencies was reduced to 10% from 23%. Comparison of the initial and updated finite element models highlighted the significance of the boundary conditions on the dynamic behaviour of the bridge.</p>

In various applications it is important to determine dynamically equivalent spatial finite element (FE) model of complex structures. For instance, obtaining the FE model of an existing aerospace structure is a major requirement for reliable aeroelastic analysis. In such applications a reliable FE model may not be always available, and when this is so a dynamically equivalent FE model derived from modal test will be very useful. This paper presents a noble method to determine spatial FE model of a structure by using experimentally measured modal data along with the connectivity information of measurement points. The method is based on the mass and stiffness orthogonality equations written using experimentally determined mode shapes and natural frequencies. These equations are solved for geometric and material properties constituting global spatial mass and stiffness matrices of an initial FE model. Starting from this initial FE model, mass and stiffness orthogonality equations are updated iteratively employing experimentally obtained natural frequencies and corresponding eigenvectors from the FE model. Iterations are continued until eigensolution of the updated FE model closely correlates with experimentally measured modal data. A simulated case study on GARTEUR scaled aircraft model is presented in order to demonstrate the applicability of the method.

Damage to civil engineering structures can be identified with a finite element (FE) model updating method using experimental modal data. In such a procedure the uncertain properties (e.g. stiffness distribution) in the FE model are adjusted by minimizing the differences between the measured modal parameters and the numerical (FE) predictions. In civil engineering the differences in eigenfrequencies and mode shapes are minimized, mostly identified from ambient vibrations. Since the modal data are nonlinear functions of the uncertain properties, an iterative sensitivity-based minimization method is used to solve this inverse problem. In order to reduce the number of unknowns, damage functions are used. The FE model updating technique is applied to a prestressed concrete bridge with 3 spans whose girder is damaged by lowering one of the intermediate piers. The damage pattern is identified (localized and quantified) by updating the Young’s and the shear modulus. Introduction Accurate condition assessment of civil engineering structures has become increasingly important. FE model updating provides a very efficient, nondestructive, global damage identification technique. The uncertain properties of the FE model are updated by minimizing the discrepancies between the measured modal data and those computed with the numerical FE model [1, 2]. The damage identification procedure is performed in two updating processes. In the first the initial FE model is tuned to a reference state, i.e. the undamaged structure. In the second process the reference FE model is updated to obtain a model which can reproduce the experimental modal data of the damaged state. The damage is identified by comparing the differences between the reference and the damaged FE model. The technique is applied to the Z24 bridge in Switzerland. It is a prestressed concrete bridge with three spans which is damaged by lowering one of the intermediate piers. A nonlinear least squares problem is solved. The residual vector contains the test/analysis differences of the first 4 bending and/or torsion modes. Frequency residuals as well as mode shape residuals are minimized. Eigenfrequencies contain global, accurate information, whereas mode shapes provide important local, but more noisy information. Therefore, both types of residuals are weighted with an appropriate factor in the residual vector. The updating parameters are both the Young’s and the shear modulus of all the girder elements. The least squares problem is solved with a sensitivity-based Gauss-Newton algorithm. In order to improve the condition of the sensitivity matrix the number of unknown parameters is reduced by using a limited set of damage functions [2]. The girder stiffness distribution is found by combining these damage functions, multiplied with the appropriate factors which are the actual variables of the minimization problem. Only linear damage functions are used, but the method can be extended by including higher order functions. With this approach always a realistic smooth result is obtained. A damage pattern is identified which resembles the observed one. The general updating procedure and the application to the Z24 bridge are presented in the paper. General FE model updating procedure Objective function. In FE model updating an optimization problem is set up in which the differences between the experimental and numerical modal data have to be minimized by adjusting the uncertain model properties [1]. The experimental modal data, i.e. the eigenfrequencies and mode shapes , are obtained from measurements. In civil engineering, the measurements are often obtained in operational conditions (ambient vibrations), which means that the exciting forces (coming from wind, traffic,. . . ) are unknown. As a consequence, an absolute scaling of the mode shapes is missing. Furthermore, only the translation degrees of freedom of the mode shapes can be measured. The minimization of the objective function is stated as a nonlinear least squares problem: