Massimiliano Gioffrè

Simulation of non-Gaussian field applied to wind pressure fluctuations

Abstract A simulation algorithm to generate non-Gaussian wind pressure fields is proposed. This algorithm uses the correlation–distortion method based on translation vector processes. Conditions on the matrix of cross-covariance functions are given to assure the applicability of the model. The proposed method does not require iterative procedures and it is well suited when experimental data are available. In particular it requires cross-covariance functions and marginal distribution that can be directly estimated from data. To illustrate the procedure, the model is calibrated on experimental results obtained from wind tunnel tests on a tall building. The efficiency of the proposed methodology for reproducing the non-Gaussian nature of pressure fluctuations on separated flow regions is demonstrated.

Estimates of extreme wind effects and wind load factors: influence of knowledge uncertainties

We propose a probabilistic methodology for developing improved load factors in standard provisions for wind loads, and use it to examine: the cause of the discrepancy noted in the 1980s between estimates of safety indices for wind and gravity loads; the relative magnitude of load factors for hurricane and non-hurricane regions; and the effect of the length of wind tunnel pressure records on the estimation of peak wind effects. According to our calculations, (1) the discrepancy between estimates of safety indices for gravity and wind loads is an artifact that can be removed by using current knowledge on probability distributions of extreme wind speeds; (2) the disregard in the ASCE 7-98 Standard of (a) knowledge uncertainties, and (b) errors inherent in the limited number of climatological data on which hurricane wind speed simulations are based, leads to incorrect wind load factor estimates; and (3) increasing beyond 30 min or even 20 min the length of pressure records used for the estimation of fluctuation peaks appears to have a relatively small effect on estimates of overall wind effects. We outline future research on wind directionality, sampling errors in the estimation of peak wind effects, and the use of probabilistic descriptions of wind effects and structural capacity to estimate probabilities of occurrence of nonlinear limit states, including structural collapse.

Numerical Analysis of Structural Systems Subjected to Non-Gaussian Random Fields

This paper deals with the stochastic response of structures loaded by non-Gaussian random fields. A finite element model is used to describe a cantilever beam assuming both linear and non-linear behavior. The cross-correlated stochastic field is generated by a numerical procedure based on the translation processes theory. The marginal distribution of the load is assumed to be lognormal and the correlation structure is based on the second-order Markov process. The statistical analysis of the results highlights the effects of the involved non-linearity and non-Gaussianity properties on the structure’s response.

Performance evaluation of monumental bridges: testing and monitoring ‘Ponte delle Torri’ in Spoleto

This paper reports the main results of the experimental approach used for identifying the structural parameters and monitoring the dynamic response to the environmental loading of Ponte delle Torri (Towers Bridge) in Spoleto, Italy. In particular, the masonry wall drillings and laboratory tests on the cores obtained are described, together with the endoscopic survey and the flat-jack tests aimed to characterize the masonry mechanical characteristics. Then, the main focus is on the monitoring system, which is constituted of displacement transducers placed on the major cracks in the piers, seismic accelerometers placed on the bridge elevation next to the bridge deck, and a system of two ultrasonic anemometers which are used to record the wind speed fluctuations simultaneously with the bridge lateral accelerations. The results obtained give useful information to assess the actual state of the bridge and can be used for future decision making in planning maintenance strategies and restoration/consolidation campaigns.

TIME VARIANT RELIABILITY OPTIMIZATION OF TALL BUILDINGS

Traditional least weight optimization of tall buildings is based on the definition of a few idealized equivalent static wind loads derived from directionless wind models. This procedure could lead to unsafe designs considering the inherently directional nature of extreme wind climates. This is especially true considering traditional models used for combining aerodynamics and site specific climatological information. Indeed these methods were developed for buildings with statistically and mechanically uncoupled systems exhibiting strong preferential behavior for certain wind directions. In this paper a recently developed component-wise reliability model is used to rigorously combine the directional building aerodynamics and climatological information. An efficient reliability-based design optimization scheme is then proposed based on decoupling the traditionally nested optimization loop from the reliability analysis. The decoupled optimization problem is solved by defining a series of approximate explicit sub-problems in terms of the second order response statistics of the constrained functions.

Microcracked bodies with random properties: a preliminary investigation on localization phenomena

Abstract In a previous paper [Comp. Meth. Appl. Mech. Eng. 2001;190:5657–5677], it has been shown that in microcracked bodies strain localization phenomena appear even if the constitutive relations are linear and the microcracks are in elastic phase and do not grow. In this paper the constitutive properties of the body are assumed random, although uniform over the body. An example case in two dimensions is presented: its properties are assumed to be the mean values or fractiles of the probability distributions of the relevant coefficients, resulting from assumed distributions of the parent quantities. In all cases, strain localization is evident; however, the influence of the random variations, at least under the set hypotheses, appears small.

Laser doppler and radar interferometer for contactless measurements on unaccessible tie-rods on monumental buildings: Santa Maria della Consolazione Temple in Todi

Non-contact measurements can be effectively used in civil engineering to assess the variation of structural performance with time. In the last decades this approach has received considerable interests from researchers working in the field of structural health monitoring (SHM). Indeed, non-contact measurements are very attractive because it is possible to perform non intrusive and non destructive investigations even being at a significant distance from the targets. Within this context, contactless measurements of the tie-rod vibrations in the Santa Maria della Consolazione Temple in Todi (Italy) are presented in this paper. In particular, laser vibrometer and radar interferometer measurements are used to estimate natural frequencies and mode shapes. This information is crucial to obtain the tensile axial force in the tie-rods, which can be used as an indicator of structural integrity or possible failure. Furthermore, a novel approach is proposed where drones (Unmanned Aerial Vehicles) can be successfully used to improve the effectiveness and the accuracy of the experimental activities.

In Situ Shear Tests on Masonry Panels Strengthened with Fiber-Reinforced Mortar Repointing

In this paper the effect of joints structural repointing on single-wythe brickwork masonry using a fiber-reinforced mortar is investigated. Changes in shear strength are evaluated by in-situ tests carried out both on unreinforced and reinforced masonry specimens. The masonry joint shear strength, according to the standard ASTM C 1513, gives local information, while diagonal compression tests provides information on the global masonry shear response. The comparison highlights a good performance in both local and global masonry response, where the shear strength increases.

STRUCTURAL MONITORING OF MONUMENTAL BUILDINGS: THE BASILICA OF SANTA MARIA DEGLI ANGELI IN ASSISI (ITALY)

Abstract. The preservation of architectural heritage and monumental structures is an important challenge of the scientific research, especially for the countries where cultural heritage is of primary concern and, at the same time, there are significant risk factors due to natural hazards as earthquakes. In this perspective, structural health monitoring systems can improve the protection of structures by providing real-time diagnostic data together with suitable procedures, which are able to identify possible occurring problems. In this work the first results given by a monitoring system placed in the Basilica of Santa Maria degli Angeli in Assisi will be presented. Data recorded by nine linear variable displacement transducers (LVDTs) are shown together with power spectral densities of acceleration time histories measured during ambient vibration tests. The spectral analysis results are compared with the natural frequencies given by a numerical model of the Basilica structural system.