Unsuitable ground conditions below the structure, for instance, can pose a threat to the integrity of a building. All structures are supported by soils or rock of different capacity and strengths.
These are not immune to failure in themselves, often caused by heavy storms, earthquakes, climate change and other environmental events. This can cause a building's foundation to fail slowly like the tilting Tower of Pisa or without warning, bringing down the structure.
My friends are unaccounted for in the Surfside building collapse, but I'm holding on to hope. Poor workmanship and badly constructed buildings, or the use of deleterious materials that do not comply with what was specified in the design, can also be a cause of failure. This can arise from undeliberate incompetence, but in rare cases can be considered criminal negligence. In the last several decades we have also seen the impact of chemical changes in materials that can cause local failure initially and then large-scale failures that, over time, render buildings unsafe.
Rusting steel expands six or seven times its original shape and when embedded in concrete it can expand and weaken the structure of a building. So, with the possibility of unforeseen events, or structural issues that are invisible to the untrained eye, how can we be sure our buildings are safe? All structures are designed with code safety factors that have been developed over decades and with much care to ensure a certain amount of safety and tolerance for accidental loads or poor workmanship.
If a building is up to code, it is generally deemed safe. This is one of the reasons put forward by civil engineers Henry Mwanaki Alinaitwe and Stephen Ekolu why a building in Uganda collapsed in Their research shows that the workers misunderstood the mixing ratios of the concrete.
It suggested that people used wheelbarrows instead of measuring gauges to measure cement. The five-storey BBJ new hotel collapsed in construction and 11 people died. To those who want to save money on professionals, he advises: "One should not be penny wise and pound foolish".
Mr Ede says a building collapses when the load is beyond the strength of the building. He gives the example of asking a baby to carry a heavy box: "The baby will not be able to withhold the strain. Even if the foundations and the materials are strong enough for what they were originally built for, that purpose may change.
So, Mr Ede says, if a building was designed to be a home and is then turned into a library where boxes and boxes of books are piled up, the building may strain under the weight. He says another reason why the load is often heavier than the original design is because extra storeys are added. In March an upmarket apartment block which had more storeys than planned collapsed in Lagos, killing 34 people the Guardian reported.
This came two years after a church accommodation for the famous preacher TB Joshua collapsed, also, authorities said, because it had more floors than it could hold. In that case more than people lost their lives.
At all points of construction the strength of the building should be tested, says Mr Ede. It's the enforcement of the law which is the problem," he says. On the diagram provided in Handout 1a, ask each student to draw a force arrow a vector and trace the path the force takes to the ground.
Review students' diagrams to ensure their understanding of the concept. Now challenge students to design and build three different arrangements of the structural elements.
Each time they modify the design, they must modify the diagram to show the new load path. Students must test the strength of their model walls to ensure survival of all floors when a force is applied.
When a structure is reinforced well, students should be able to push on the upper story and slide the whole structure without any of the walls failing. Note: There are many possible configurations which will produce a structure that can resist applied forces.
However, the minimum configuration must include a continuous load path from the upper left hand corner down to the base of the structure. Invite students to discuss the questions listed in Handout 1b. Ask one student per group to record each group's response. After all groups finish the questions, have a spokesperson from each group present students' responses to one of the questions.
Allow the class to come to some consensus on their responses to that question, and then proceed to another group until all the questions have been discussed. Caution: Discuss with the students the similarities and differences between the wall model and what real walls experience during an earthquake.
The primary difference is that whereas earthquake surface waves shake buildings back-and-forth horizontal and up-and-down vertical , this model only simulates horizontal forces. In addition, the shaking motion of an earthquake applies forces with changes in direction and magnitude in a complicated way, but this model is best for studying steady, unidirectional applied loads. These are also known as "static" loads while changing loads are known as "dynamic" loads.
Explain to students that seismic engineers use similar methods to provide earthquake reinforcement for existing buildings. Engineers tend to use a combination of techniques to complement the strengths and weaknesses of each approach, which include the use of diagonal braces, shear walls, and rigid connectors. Diagonal braces craft sticks in this activity are usually built into a wall to add strength.
Shear walls cardboard pieces in this activity are added to a structure to carry horizontal shear forces. These are usually solid elements and are not necessarily designed to carry the structure's vertical load.
Rigid connections paper clamps in this activity do not permit any motion of the structural elements relative to each other.
Conclude this activity by helping students connect the behavior of their model walls to their mental images of real buildings during an earthquake. Emphasize that the back-and-forth motion, the horizontal component of ground shaking, is the force most damaging to buildings. Buildings are mainly designed to carry the downward pull of gravity, but they need to be able to withstand sideways, or horizontal, pushes and pulls in order to withstand earthquake shaking.
Aa Aa Aa. Lesson 9: Structural Hazards. This lesson will introduce students to some of the basic concepts behind structural hazards in the context of earthquakes. Many cities have a variety of building sizes, shapes, architectural styles, and materials. This lesson covers the basic ideas concerning how structures respond to earthquakes using a tabletop exercise and three hands-on activities. The tabletop exercise consists of visual analysis of actual pictures taken in earthquake areas in Central Asia.
The hands-on activities will explore how structures respond to applied loads. Begin by reviewing with the students the two basic types of earthquake waves: P and S waves. Compare and contrast their differences P waves are compressional, longitudinal waves and generally less destructive than S waves; S waves are transverse waves that move perpendicular to the path of propagation. Surface waves, a combination of both P and S waves, cause most earthquake destruction because they lead to wave-like motion along both the horizontal and vertical axes, which cause structural damage.
Please refer to Lesson 6 for more information about seismic waves. Figure 1: Different applied load types. Tabletop Exercise: Uncle Architect. To get the file for pictures, click here. Read the following scenario while stopping to ask questions and discuss the material with your students at the indicated points or when students ask questions that are relevant to the discussion of earthquake hazards: Sami lives with his family in a city.
At first, there were so many pictures that Sami didn't know where to start. Question 1: What are some of the ways that the pictures can help Sami explore why some buildings can stand through earthquakes while others collapse? Why is it important to take notes that accompany the pictures? Question 2: Compare pictures 1 and picture 2. What is the same and what is different about the construction styles and materials? What are some possible reasons why the buildings in picture 1 did not fully collapse, but those in picture 2 did?
Question 3: Look at pictures 3 and 4. What other objects in the picture, besides buildings, did not collapse during the earthquake? What features of these objects made them likely to survive while other buildings collapsed?
Are there other hazards associated with these objects that are different from the hazards associated with buildings? Question 4: Look very closely at the buildings in pictures 4, 5, and 6. What is different about these buildings, and why would these differences help them to better survive earthquakes? Question 5: Compare pictures 7 and 8. What is different about the roofs of these buildings compared to the roofs of the buildings in other photos?
Why might these roofs survive an earthquake better? Question 6: Look at the close-up of the roof attachment in picture 8. What do you think bothered Sami about the way the wooden roof beam sits on the column? How would you design the column attachment differently for earthquake-resistance? Tabletop Experiment: Building and Reinforcing Structures. Now that students have had a chance to observe and think about actual structures that have or have not survived earthquakes, they have the opportunity to explore structural hazards and mitigation techniques in the following 3-day lesson.
On Day 1, students build model structures and describe what may happen to them when a load is applied. On Day 2, students build and test models on a shake table to understand how a structure reacts to vibrations of different frequencies as well as explore the phenomenon of resonance. On Day 3, students build a model wall to learn how structural elements such as diagonal braces, shear walls, and rigid connections strengthen a structure. Day 1: 1 set of styrofoam blocks, various sizes Pieces of string, each 30 cm long Paper clips Toothpicks A brick or a heavy item A band saw to cut styrofoam Drinking straws Straight pins Day 2: 1 earthquake shake table here 1 set of wooden blocks, various sizes 1 set of styrofoam blocks, various sizes Day 3: Copies of Handouts 1a and 1b one per group To get the file for the handouts, click here.
It is recommended, whenever possible, that the students are involved in the construction of the setups. Procedures: Day 1. Provide each group with pieces of styrofoam, strings, paper clips, and toothpicks. Explain to each group that they are a team of seismic engineers and are expected to build the strongest structure possible given the materials listed above for Day 1 activities.
Tell them they have 20 minutes for this activity. This activity is designed for students to have some fun, and their efforts should not be criticized. Procedures: Day 2. Provide each group with a set of wooden blocks. Ask each group to build a simple structure, but it should be strong enough to survive the vibrations of a shake table. Explain to them they can use as many blocks as they want to build their structure.
Allow 10 minutes for this part of the activity. Procedures: Day 3. Tell students they are going to assemble a model wall and predict what would happen if they push the base of the wall simulating an earthquake. They are then given materials to reinforce their model and test again.
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