# Questions tagged [structures]

Questions relating to or the engineering application of a device that must withstand a loading via deflection, stresses, resistance to buckling, or natural frequencies.

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49 views

### Wind Pressure on Chimney

I have this question that I am trying to solve. I cannot put diagram up to show problem because it is over file size limit of 2 MegaBytes, but I will explain problem as best as I can. A brick chimney ...
19 views

### Techniques to make residential buildings more blast resistant

There are generally two approaches: First: use stronger materials (e.g. thicker RCC with fibres, go underground, etc). Second: for any given material, use a superior design. The First approach is ...
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### I'm Missing Something on Problem 3 in Section A5.4 of Bruhn's Analysis and Design of Airplane Structures

I've been working through the 1943 edition of Bruhn's Analysis and Design of Airplane Structures. I found an archive.org pdf version of the 1948 edition that includes answers to select problems, as ...
1 vote
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### Structure's equlibrium state

The state problem of a structure at equilibrium is generally expressed as: $K(x) ~u = F(x)$ where $K$ is the stiffness matrix, $u$ is the displacement vector, $F$ is the force vector, and $x$ is the ...
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### Transmitting load to a fixed support of a structure

In structural optimization, we try to design our structure in a way to sustain loads in the best way possible. An example could be thinking about transmitting loads to fixed supports in an optimal way....
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### Shape of a beam that is bowed under compression?

Suppose you have a uniform beam, such as a piece of plywood that is 4 feet long, six inches wide, and half an inch thick. Suppose you cause it to bend by attaching, for example, a string under ...
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### Counterweight requirement and platform design for motorised speaker stand stability

I recently bought my dream speakers (Dutch & Dutch 8c), but at the cost of having to preserve a minimalist interior for the sake of household peace. To that effect, I plan to construct motorised ...
37 views

### How is the number of memebers in a truss calculated?

In a fully connected truss (each node connected to all other nodes), the number of members (bars) is equal to $n(n−1)/2$ where $n$ is the number of nodes. I don't understand the derivation of this ...
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### Should a house wall be perpendicular to the direction of a strong wind carrying rain water?

I am building a perfectly squared single-storey house (10m x 10m). To have the best output from the solar panels, which should face South as straight as possible, the external South facing wall of the ...
1 vote
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### How did gothic church architects/builders properly scale up their models to full size churches?

In this video the author explains how ancient church builders used models to determine the proper shape and order of installation of architectural elements in gothic churches. From the little I know, ...
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### How to design safely collapsing buildings?

Background—Currently, buildings seem to be designed to be strong enough to not fall upon dangerous events, such as earthquakes. This makes them expensive, and out of the reach of poor places. Poor ...
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### Beam deflection for FEA model validation

I'm trying to validate an FE model that I'm using by comparing to a simplified analytical solution to the problem. The part I'm analyzing is a lug that is constrained on one end and has a point load ...
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### Does yield point of steel depend on thickness?

I have two different plates of different thickness and I need to calculate yield point. Does yield point of steel plate changes with changing of plate thickness?
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### Calculating the plastic section modulus, Z, of an arc of a circle

I am trying to find a simplified formula for determining the plastic section modulus, Z, of an arc of a circle. In my case, I have a 20" diameter 0.375" thick pipe and I am cutting a 6" ...
1 vote
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### Lateral load calculation at the bottom of an arch

I am trying to find out how much lateral thrust an arch produces when applying a load evenly distributed across its span. There are a lot of 'complex' models around and full analysis done case by case ...
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### How is a room structurally suspended above a garage cutout?

The garage of this cavity wall (outer brick layer wall, inner concrete load bearing wall) new build uk house is a cutout directly below a room. i'm confused because this obviously interrupts the ...
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1 vote
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### Is the AISC's Steel Construction Manual's out of plane "special case" valid for all weld groups?

In the AISC's Steel Construction Manual Table 8-4 "Coefficients C for Eccentrically Loaded Weld Groups", it mentions the Special Case where the load is not in plane with the weld group. ...
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### Rectangular pressure vessel

I'm trying to find a theory reference for stress and deformation analysis of a closed rectangular pressure vessels with constant thickness subjected to pressure loads. By now, my test case would be ...
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### How long would it take for the Brooklyn Bridge to collapse if the four main cables were cut where they connect to the ground? [closed]

How much time would the people on the Brooklyn Bridge have to get off if all four main cables failed simultaneously? Are we talking about an immediate collapse the second the cables are severed, or ...
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### Structure Grid for a building with irregular shape

I am making a building block with the shape as outlined in yellow in the attached capture, as for the structure I am not sure how to place the loadbearing poles and I could use some help
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### Looking to make a retractable disco ball

I am looking to make a disco ball that sits in its normal position, attached to a ceiling, but to be able to hit a switch and it track upwards at a 90° angle to be hidden horizontally in a case. I am ...
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### Displacement as a function of the force and the properties of the frame I and J

I was wondering how you would find the stiffness matrix of a triangular frame with unknown angles. A little context The pumpjack model involves a triangular frame on which the rocking beam is ...
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### Calculation of Drone Fuselage Natural Frequencies

I'm looking to do a frequency analysis of a fixed-wing drone. The goal is to calculate the first few natural frequencies of the fuselage to verify there is no resonance with the wing structural/...
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### Jibs fastening in a frame structure

I need to make a demountable frame for cycling trials: I want to make it based on steel profile square tubes: The design must have variable dimensions and slopes. I guess provide variable dimensions ...
229 views

### How to support the columns of a second level of an hypaethral building with reduction in space by height?

In this multi-leveled hypaethral building model there is a problem that the columns of the second floor aren't directly situated on the columns of the first floor. How to support the columns of the ...
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### With respects to the North Channel (Irish Channel), has a causeway ever been proposed for a crossing?

Former UK Prime Minister, Boris Johnson raised the issue of a bridge between Scotland and Northern Ireland; his impromptu estimate of £15 billion was probably a little wide of the mark. The issues are ...
239 views

### Flat slab main bar direction longer or shorter

In flat slab system, say that the total length is 48m x 24m, column with drop panel with spacing of 6m... In this case , main bar outermost top bar (T1) and outermost bottom bar (B1) should be ...
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### Fish tank stand - confirm if steel material will be suitable

Hi I would like to make a fish tank stand like the one in the photo. I have been scouring the internet for an answer to how thick the material I select should be, in either SHS or RHS. I was thinking ...
247 views

### What will the reaction forces of a support be in case of an angled cable

If a cable is attached to a support on each side, and there is a load acting on it somewhere along its length. Is there going to be a vertical reaction force only if the the cable is angled?
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### Compound angle for support tri-beam / double knee brace

I'm trying to determine the most structurally sound way to construct a support beam for a serious treehouse. There are four options I've mocked up below - the first two are individual knee brace ...
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### Resultant Forces in a vertical rod

This is a pretty basic question. So in the below figure is the representation of prismatic column. The forces are represented as P1 and P2. let x be an arbitrary cross section between A and B. The ...
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### is a rebar arch structure a good idea?

I am thinking of building a simple shaded Arch for agriculture. I have an idea of building it with 30 ft sections of rebar that I will bend into a rough art shape. I would then weld rebar ...
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1 vote
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### Why are these food stretch films (LLDPE) holding one one-thousandth of the weight in reality than what is expected from the datasheet values?

I am trying to reproduce analytically the results found in this experiment where a weight of 3 x 5 lbs (6,8 kgs total) breaks the cling wrap (LLDPE) which is stretched over a medium size cooking pot. ...
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### How to measure strength of stretch film on a mock up

Let's say I have an iron cube of 1 cubic meter and I want to make an aquarium out of it. To hold water I want to wind stretch plastic film around the walls of that experimental aquarium. Let's assume ...
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### Force that a surface made of stretch film can sustain

I need to estimate the static spread force (Newton) that a plastic wrap wound around a given square frame (1 sq meter) can sustain. The stretch film has a given thickness (eg 17 microns ~ 63 gauge) ...
65 views

### Does the weight of a pilot exponentially affect the necessary weight of human-powered aircraft?

The MIT Daedalus, a human-powered craft, weighed about 31 kg. This was significantly lighter than its pilot during its record setting trip, though I can't confirm the pilot's exact weight. Still, this ...
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### What is the most structurally supportive 3D Tessellation? The sort of thing you'd use to build chambers for an underground mansion

Hexagons are considered the strongest grid pattern, I believe, and that's why bees use them? They're an efficient use of space, with maximal structural integrity. I was wondering what a 3-dimensional ...
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### How did this building's windows get like this?

I don't recall seeing the walls like this before, so I don't think it's just accumulated soilage. If it's wetness, what design flaw causes the windows to do that? Today was very hot and muggy so it's ...
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### Square box welding with T joint, welded with stick welding

When joining two square box beams in Tee, is it enough to weld them in only three sides or I have to weld the full perimeter of the square? If those 3 sided weld are suppose to bear weight, how much ...
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### Mechanism and static determinacy

I was doing exam question and am confused as to how to determine if the structure is a mechanism or not. Say that j = number of joints, r = total number of reactions, b = number of bars. For both (a) ...
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1 vote
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### Symmetry to determine the support reactions of a statically indeterminate frame

The following is an indeterminate frame consisting of two beams that are rigidly connected to each other at the corner support. I want to find the support reactions. As far as I can see, this is a ...
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### What is the cause of this cracking pattern in a simply supported beam?

Background On May 5th 2022, a bridge was struck in Brantford, Ontario, Canada by a commercial vehicle. This vehicle struck a reinforced concrete protection beam placed on the on-coming side for the ...
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### Is it valid to solve for the young's modulus required for a given critical load with Euler Columns?

I am working on a problem for research that is about material choices. I was wondering if the following rearrangement of Euler columns would be a valid way to check to see if a material exists for a ...
281 views

### Analysing a multispan determinate beam by separating it into spans

Say we have the following indeterminate beam: We can make it determinate by adding a pin at B, and then adding back the bending moment at B which was destroyed by the pin: My lecture handouts then ...
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1 vote
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### Steel bracket fixing spacers on a wall

What could I do to address the uneven vertical wall (not plumb) behind the bottom of the steel bracket? Would you fill in the gap with sand/cement and once dried tighten the bolt or use steel plates ...
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### How do you calculate the maximum bending stress in a beam with different thickness along different parts on the beam?

Here is a practise question that I am working on. The beam has different thickness due to the supports in the middle. I would expect the maximum bending stress be away from the middle due to the ...
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### If you have unlimited space, how many toilets can you put into a public restroom? [closed]

Are there structural limits or legal limits of any kind?
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### How many more degrees of tilt can the Millennium Tower in San Francisco withstand before it becomes structurally unsound? [closed]

How many more degrees of tilt can the Millennium Tower in San Francisco withstand before it becomes structurally compromised/unsound? "...An examination in 2016 showed the building had sunk 16 ...
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