Rigid Block Analysis to Assess Settlement Induced Damage Progression in Masonry Façades

Nathan Taylor and Ryan Ehresman Author

04/05/2021 Added

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Our research shows our progress in determining the structural behavior of masonry buildings over time. We utilized the discrete element model to simulate individual brick behavior and conclude the overall results of a full masonry façade.

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[00:00:00.810]Hello, this is Ryan Ehresman, and this is Nathan Taylor.
[00:00:04.410]The focus of our undergraduate research project is analyzing the behavior of
[00:00:08.430]rigid blocks using the discrete element method to discover the effect of
[00:00:11.970]settlement damage over time on masonry facades.
[00:00:16.260]Starting with an introduction to the history of masonry structures,
[00:00:19.380]Unreinforced masonry construction and architecture was very popular in the 18th
[00:00:23.880]and 19th centuries. Even making its way into the 20th century.
[00:00:27.660]It's abundance during the Romanesque era of architecture made it popular in many
[00:00:31.380]urban areas, such as downtown Omaha. Walking through downtown Omaha,
[00:00:35.400]you can see multiple aged brick walls giving the area a historic texture.
[00:00:40.020]These buildings represent the history of Omaha and maintaining their structural
[00:00:43.680]stability will help keep that historic texture alive.
[00:00:47.160]The beauty of masonry is that it is also used in rural settings,
[00:00:50.430]such as the Gage County courthouse built from 1890 to 1892 in Beatrice,
[00:00:55.110]Nebraska. It was registered as a national historic structure in 1990,
[00:01:00.060]proving the community wants to preserve these historic structures.
[00:01:04.910]Some of the major structural properties of masonry are shown on this slide.
[00:01:09.650]First and foremost,
[00:01:10.880]brick is a material that is weak in tension and strong in compression.
[00:01:15.230]This means that it can withstand a great deal of load when the brick is squeezed
[00:01:18.860]together,
[00:01:19.580]but much less when the brick is pulled apart. This weak tensile strength results
[00:01:23.840]in structural problems, such as cracking, Joint dislocation, and sliding failure.
[00:01:29.030]Secondly, masonry is a heterogeneous material,
[00:01:32.270]meaning the different points on the wall have different structural makeup and
[00:01:35.690]different structural capacities. Since spots on the wall are different,
[00:01:39.710]it makes it very hard to predict where failure will occur. Lastly,
[00:01:44.360]masonry walls often have slight differences in their morphological properties of
[00:01:48.530]geometric patterns, which make them hard to analyze.
[00:01:53.510]Knowing the flaws of masonry and the difference caused by varying patterns of
[00:01:57.140]bricks is important for predicting the behavior of the structure as a whole.
[00:02:00.890]We made this prediction by simulating each individual brick's,
[00:02:04.070]sliding and rotational motion by applying the equations of motion from physics.
[00:02:08.780]Using these individual simulations to measure the group's interaction is a
[00:02:12.680]process called the discrete element method.
[00:02:16.760]Using the discrete element method allowed us to predict multiple types of
[00:02:20.930]behavior within the brick wall.
[00:02:23.120]There are numerous interactions that we can model such as sliding, joint opening,
[00:02:27.740]and separation.
[00:02:29.360]One big advantage that discrete element modeling has over field experimental
[00:02:33.170]studies is that we can understand the internal behaviors such as motions and
[00:02:37.580]forces much easier if it is being calculated through a computer.
[00:02:42.470]Lastly,
[00:02:43.010]another advantage of discrete element modeling is that repeating the equations
[00:02:46.820]over and over simulates a realistic behavior.
[00:02:50.390]And that can be proven as in our research.
[00:02:55.130]All of these simulations are very valuable,
[00:02:56.690]but understanding what is causing the structural failure of
[00:02:59.260]cracking is important as well. Settlement damage stems from the ground
[00:03:03.250]reacting to the weight of the building on top of it.
[00:03:05.710]The soil underneath compresses and leaves the building on uneven ground or
[00:03:09.550]causes air pockets underneath the surface.
[00:03:12.010]These unbalanced conditions cause large amounts of stress in the structure.
[00:03:16.270]This extra force within the facade often causes cracks to populate at joints,
[00:03:20.800]such as corners of doors and windows, as well as spandrel in between windows.
[00:03:25.720]The arrows shown on our images represent where the settlement would be occurring
[00:03:29.380]on the bottom of the structures.
[00:03:32.970]In our research,
[00:03:34.230]we validated that the settlement applied to a building from Giardina et al.'s
[00:03:38.580]study could be modeled by the discrete element method. To do this,
[00:03:42.450]we populated an AutoCAD model with the exact same facade as the study.
[00:03:47.370]After populating the model in AutoCAD,
[00:03:49.320]we wrote a code that would apply a soil settlement to the building and evaluate
[00:03:54.120]this settlement using a software which runs the discrete element method.
[00:03:58.350]As you can see, after applying settlement to our model of the facade,
[00:04:02.310]the building showed very similar patterns of displacement quantitatively on the
[00:04:06.870]graph.
[00:04:08.010]Also the building cracked in a very similar way to the actual lab facade.
[00:04:12.810]You can see this picture to show the qualitative similarities as well.
[00:04:18.840]Once we generated a successful code,
[00:04:20.760]we wanted to confirm the effects of stress and friction on a masonry facade.
[00:04:24.810]We used sensitivity analysis,
[00:04:26.490]which allows us to control the values of our target parameters to see their
[00:04:30.030]overall effect on displacement.
[00:04:32.310]Our graph results show that tension causes more deflection horizontally due to
[00:04:36.120]the weak tensile strength of masonry causing cracks before bricks could slide.
[00:04:40.680]This sliding failure is needed for friction to heavily affect displacement,
[00:04:44.490]so our tension parameter caused a larger fluctuation of displacement overall.
[00:04:48.630]The vertical displacement changes are less noticeable,
[00:04:51.600]but tension still results in a larger overall change.
[00:04:54.990]That also means that strong mortars that can handle the tensile strain and
[00:04:58.710]constant maintenance are necessary to preserve these historic masonry buildings.
[00:05:04.110]After validating the discrete element method work and fine tuning
[00:05:07.470]the appropriate mortar strength parameters, we're in the process of evaluating
[00:05:11.580]how soil settlement affects this building facade from the Happy Hollow Coffee
[00:05:16.320]building in downtown Omaha.
[00:05:18.810]As you can see, the picture on the right is an AutoCAD model of the building.
[00:05:23.880]We are now in the process of writing code and evaluating that code using the
[00:05:28.560]discreet element method. After that, we will gather data,
[00:05:32.880]finish our journal article and publish the results.
[00:05:38.160]Our conclusions up to this point include that utilizing the rigid block analysis
[00:05:42.210]with the discrete element method is both applicable and accurate in examining
[00:05:46.500]the settlement damage of masonry structures
[00:05:48.990]as we proved comparing our results to Giardina et al.
[00:05:53.280]Also in our parametric analysis results,
[00:05:55.860]we found that greater tensile strength results in less deformation compared
[00:05:59.930]to low bond tensile strength,
[00:06:01.910]whereas frictional resistance was of lesser importance for settlement induced
[00:06:05.890]damage.
[00:06:07.840]And finally, masonry buildings that are susceptible to cracking require
[00:06:11.920]maintenance that should be done consistently.
[00:06:15.370]Lastly, we would like to acknowledge and thank all of the people in the UCARE
[00:06:19.510]program, Dr. Bora Pulatsu, and Dr.
[00:06:22.210]Ece Erdogmus for allowing us this opportunity to conduct undergraduate
[00:06:26.980]research. Thank you to all.

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Rigid Block Analysis to Assess Settlement Induced Damage Progression in Masonry Façades

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