Blast Retrofit of Unreinforced Masonry Walls Using ECC Shotcrete
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Résumé
Blast loads on buildings can originate from accidental explosions or from targeted attacks. Design against blast loads has become an increasingly important topic due to the current political climate. Unfortunately, many older buildings are constructed with unreinforced masonry (URM) walls which are particularly susceptible to out of plane failures caused by blast loads. One solution to increase the safety of these buildings is to retrofit them with advanced materials that can increase their out-of-plane stiffness and resistance. This thesis investigates the potential of using a high-performance shotcrete as a retrofit system for URM walls against blast effects. The shotcrete used in this study is made from Engineered Cementitious Composite (ECC), a special type of fiber-reinforced cementitious material, with high ductility and high energy-absorption capacity. The ECC shotcrete replaces aggregates with synthetic microfibers to increase tensile strength and ductility. A welded wire mesh was embedded in the shotcrete to provide ductile behavior. The testing program includes a total of six large-scale unreinforced masonry wall specimens. Two walls were constructed using concrete masonry unit (CMU) blocks to be retrofitted. The first specimen was built as an infill wall, experiencing no axial load, while the second specimen was built as a load bearing wall, with 10% axial load. Four more walls were built out of stone blocks. Two of the stone walls were controls: one infill and one load bearing (4% axial load). The other two stone walls were retrofit with the shotcrete system: one infill and one load bearing (4% axial load). The blast loads were simulated using the University of Ottawa’s Shock Tube. The walls were restrained at the top and bottom with a shear restraint to induce one way bending. Pressure, displacement and strain data were acquired with the use of pressure gauges, LVDT’s, strain gauges and cameras. The specimens were subjected to gradually increasing blast pressures until failure. The performance of the specimens was observed by analyzing the displacement, crack widths, fragmentation and failure mode. The results indicate the benefits of using ECC shotcrete as a retrofit system. The displacements of the retrofit walls were very small compared to the control walls, and fragments were limited. The specimens with axial load were found to have increased resistance. While the failure mode was brittle for the retrofit walls, this can be avoided with the use of a mesh with a larger area of steel. A SDOF analysis was performed to predict the blast response of the test walls. The analysis was done by generating resistance functions for the walls through analytical models. The analysis was found to agree reasonably well with the experimental data.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle