Experimental and FEM Investigation of Cob Walls under Compression

Earth has been used as construction material since prehistoric times, and it is still utilized nowadays in both developed and developing countries. Heritage conservation purposes and its intrinsic environmental benefits have led researchers to investigate the mechanical behaviour of this material. However, while a lot of works concern with rammed earth, CEB, and adobe techniques, very few studies are directed towards cob, which is an alternative to the more diffused rammed earth and adobe in specific geographic conditions. Due to this lack, this paper presents an experimental program aimed at assessing the failure mode and the main mechanical properties of cob earth walls (compressive strength, Young's modulus, and Poisson's ratio) through monotonic axial compression tests. Results show that, if compared with CEB, adobe, and rammed earth, cob has the lowest compressive strength, the lowest modulus of elasticity, and Poisson's ratio. Differences are also found by comparing results with those obtained for other cob techniques, underlining both the high regional variability of cob and the need of performing more research on this topic. A strong dependence of material properties on loading rate and water content seems to exist too. Finally, the ability of a common analytical method used for masonry structures (an FEM macromodelling with a total strain rotating crack model) to represent the mechanical behaviour of cob walls is showed

How to restart? An agent-based simulation model towards the definition of strategies for COVID-19 "second phase" in public buildings

Restarting public buildings activities in the "second phase" of COVID-19 emergency should be supported by operational measures to avoid a second virus spreading. Buildings hosting the continuous presence of the same users and significant overcrowd conditions over space/time (e.g. large offices, universities) are critical scenarios due to the prolonged contact with infectors. Beside individual's risk-mitigation strategies performed (facial masks), stakeholders should promote additional strategies, i.e. occupants' load limitation (towards "social distancing") and access control. Simulators could support the measures effectiveness evaluation. This work provides an Agent-Based Model to estimate the virus spreading in the closed built environment. The model adopts a probabilistic approach to jointly simulate occupants' movement and virus transmission according to proximity-based and exposure-time-based rules proposed by international health organizations. Scenarios can be defined in terms of building occupancy, mitigation strategies and virus-related aspects. The model is calibrated on experimental data ("Diamond Princess" cruise) and then applied to a relevant case-study (a part of a university campus). Results demonstrate the model capabilities. Concerning the case-study, adopting facial masks seems to be a paramount strategy to reduce virus spreading in each initial condition, by maintaining an acceptable infected people's number. The building capacity limitation could support such measure by potentially moving from FFPk masks to surgical masks use by occupants (thus improving users' comfort issues). A preliminary model to combine acceptable mask filters-occupants' density combination is proposed. The model could be modified to consider other recurring scenarios in other public buildings (e.g. tourist facilities, cultural buildings).Comment: 21 pages, 16 figures; submitted to Building and Environmen

flooding risk in existing urban environment from human behavioral patterns to a microscopic simulation model

Abstract Climate changes-related floods will seriously strike population in existing urban environment. Despite Current assessment methods seem to underestimate the human behaviors influence on individuals' safety, especially during outdoor evacuation. Representing pedestrians' evacuation would allow considering the "human" factor in risk analysis. This work proposes a flood-induced pedestrians' evacuation simulation model, based on a combined microscopic approach. Behavioral rules, obtained by real events videotapes analyses, are organized in an agent-based model. Motion criteria proposals are based on the Social Force Model. Experimental motion quantities values are offered. The model will be implemented in a risk assessment simulation tool

Seismic risk of Open Spaces in Historic Built Environments: A matrix-based approach for emergency management and disaster response

Abstract Earthquakes affect the safety of the users hosted in both indoor and outdoor urban built environments, especially in Historic Built Environments (HBEs). Many full HBE-scale risk-assessment methods are defined, while methodologies oriented to local analysis of meso-scale elements, such as Open Spaces (OSs), are still limited. Nevertheless, OSs play a crucial role in the first emergency phases, like in the evacuation process, since they host emergency paths and gathering areas. The seismic risk of an OS mainly depends on the combination of the damage suffered from facing buildings and the exposure, which mainly refers to the quantification of human lives. Damage levels result from the combination of vulnerability and hazard-related issues, while exposure is essentially affected by the number of OS users, whose spatial distribution is strongly time-dependent. Methods to quickly combine these issues are needed, especially in view of the deeper insights for the implementation of risk-reduction strategies (i.e. according to simulation-based approaches). This work offers a novel methodology to quickly perform Seismic Risk Assessment and Management of an OS by correlating damage levels to exposure-related issues. The method is composed of two specific matrices, which are developed according to quick literature-based approaches prone to rapid meso-scale applications in HBEs, also by non-expert technicians. The "damage matrix" links the site hazard to the building vulnerability. The assessed damage levels are combined with the users' exposure into the "consequences matrix", to estimate the risk in emergency conditions for the OS users, thus supporting decision-makers in promoting robustness/preparedness strategies

Greenery as a mitigation strategy to urban heat and air pollution: a comparative simulation-based study in a densely built environment.

The urban heat island and the urban air pollution concentration are two major climate-change-related phenomena affecting the built environment worldwide. This paper aims to verify the potential effect of different mitigation measures through a simulation study. In detail the present study focuses on the analysis of the environmental impacts of urban vegetation, such as green facades, vertical greenery, and green pavements. After an extensive screening of the literature review, an investigation of the impact of the most common built environment design variables in a defined case study led to the definition of a typical urban canyon was tested. The results show that the presence of trees in a street canyon could reduce the air temperature peaks by 5-10 °C, while the high-level vegetation canopies can lead to a deterioration in air quality with a PM concentration increasing by 1.2-1.5%. Instead, using low-level green infrastructure improves the air quality conditions on the sidewalk, reducing the NOx in the range of 10-20%. The analyzed high-level greenery generated an air temperature reduction effect on a street level ranging from 8 to 12°C. The present work contributes to clarifying the potential mitigation effect of green infrastructure in a densely built environment, where the risk of increasing temperatures and air pollutants is foreseen to be more intense in the coming years

Cob Construction in Italy: Some Lessons from the Past

Raw earth is a construction material unknown to most people. Nowadays, raw-earth constructions are an area of growing interest, both for rescuing the heritage and for a rediscovered environmentally friendly building and eco-sustainability material. However, because raw-earth constructions are a forgotten technique, we find problems of a lack of skilled people at all levels in this area, from designers to masons, as well as problems of how to carry out compatible conservation works on earthen heritage. This paper tries to fill the gap for a peculiar historic earthen building technology, namely cob (or bauge), which is present in Macerata in the center of Italy. Results are presented on regaining possession of the material and constructional aspects and their initial structural resources, and guidelines are given on how to improve the manufacturing process to reuse the cob technique for construction and for how to accurately work on it for a compatible and sustainable conservation

Determining behavioural-based risk to SLODs of urban public open spaces: Key performance indicators definition and application on established built environment typological scenarios

A behavioural-based approach can be used to assess how users’ reactions to surrounding environmental conditions can alter the urban Built Environment (BE) risk to Slow Onset Disasters (SLODs). Public Open Spaces (POSs) in the BE are relevant scenarios, due to micro-climate-related stress, users’ vulnerabilities (e.g., age, health frailty) and exposure time. Simulation methods can support behavioural-based risk-assessment, but results are generally site-specific. Performing analysis on BE Typologies (BETs) can improve robustness, since BETs represent archetypes from real-world scenarios. This work adopts a behavioural-based approach to evaluate time-dependant users’ risks of POSs in different BETs due to SLODs-related stress (i.e., heat, air pollution). UTCI and AQI values are mapped within each BET. Users’ distributions are then calculated depending on thermal acceptability correlations. Key Performance Indicators are developed associating users’ distribution to SLODs effects on health (i.e., sweat rate, water loss; health affection rate probability). The approach is applied to Italian BETs, under one relevant climate, rating their heat and air pollution risks. Results suggest critical conditions for toddlers. In detail, about 2-hour high heat exposure could result in dehydration, while 1-hour exposure to low NO2 concentration could result in +1% mortality probability. This approach could potentially support decision-makers on BE risk-assessment

design of a smart system for indoor climate control in historic underground built environment

Abstract The application of sensors-actuators networks in Building Heritage can lead to significant improvement in indoor climate control, with the aim to both reduce energy consumption, and improve conditions for occupants and hosted Heritage. This study proposes the preliminary design of a smart indoor climate control system, based on low-impact application criteria, which can be applied to visited underground built environment. The system is based on the balance of hygrothermal loads. Sensors and actuators requirements are defined, and control algorithm are based on the comparison between real-time monitored and "natural" temperature and hygrometric values (for stationary and transitory conditions)

Superfici autopulenti e biocide nel restauro archeologico di pietre e laterizi

Archaeological artifacts are inevitably subject to deterioration caused by natural air pollution, contaminants by human actions, and biodeterioration from microorganisms. Their preservation is considered a more and more strategic factor in many countries because of their economic, social and cultural implications. Modern techniques of interventions often require re-application after some years, and they cannot be used in all restorations. Recently, the use of nanotechnologies was transferred to the restoration sector bringing many innovations. Titanium dioxide (TiO2) is the main nanostructured material used to prevent the comparison of weathering traces, to obtain self-cleaning materials and to slow down biofouling as well. In this paper, its potential use was tested on common archaeological materials like sandstone, limestone and bricks. The self-cleaning ability of this innovative material, as well as, its biofouling prevention were evaluated in laboratory simulated tests. Results show the high potentiality of this nanomaterial in making the tested archaeological surfaces self-cleaning and biocide