# Tag Info

## Hot answers tagged structures

38

They are called bollards. Their function is to provide safety for pedestrians from traffic, distracted drivers who may encroach into the sidewalk, or runaway cars e.g a driver who inadvertently leaves his/her car in neutral without the emergency brake set. Many municipalities require them and have codes and specifications defining their dimensions and ...

28

They are called Bollards. But these aren't defensive as suggested. Look closer. There's no curb. This is a new style of store (from the architecture) and curbs have been eliminated for ADA reasons (benefit of wheelchairs). As such, there is literally nothing to prevent a car from drifting forward and hitting the building; it's not even clear where you ...

22

Most bridges (and overpasses) are built to cross over something. With a few notable exceptions, most of these "somethings" are relatively long perpendicular to the desired crossing direction and fairly narrow parallel to it. Therefore a simple "two directional" bridge best meets the needs of the engineering problem. Engineers always try to solve a problem ...

14

Pedantic Answer First You specifically eliminated most constraints that would make this anything other than an theoretical exercise. You did specify that it had to be "built" though. By building something, you have to physically move the top piece into place. This means that the entire structure will have been slightly taller than the final condition, i.e. ...

11

Any limit is going to be hard to quantify. There are a lot of factors that have to be weighed when choosing the basic material type. The short answer is that the limit has already been chosen for each building. This was done during the design by the architects and engineers that worked on the building. Some of these decisions might have depended on the ...

11

This marketing video shows moments of their construction. At 0:40 you can see them all upright. They aren't painted, but you can tell it's the same installation. At 1:37 and 1:46 you can see guys drilling into the boulders From 2:16 to 2:24 you can see the base is also being drilled and, most clearly, steel rods are being slid into the rocks. So it is ...

10

How To Read the Graphs The graphs are plots of stress versus position. Stress is the force per unit area exerted on a material. Positive values are tension and negative values are compression. The first (leftmost) plot shows the normal stress vs. position that would be expected from bending if there was no pre-stress. The middle plot shows the pre-...

10

For example, take a look at the following static systems. Assume they have the same length and the same (constant) cross-section. Thus an equal allowed bending moment $M_u$. The first system is statically determinate, as it is supported only by simple supports. The maximum moment developing within the beam is $M=\frac{QL}{4}$, thus the load under which the ...

9

What is the difference between a Live or Dead Load? A Live Load is typically a moving load. This can be vehicles on a bridge or occupants and vehicles in a building. Dead loads are (relatively permanent loads). These are simple ways to differentiate the type of load, but why do we care? The basic answer is, "Because the Code cares." Why does the Code ...

9

I suspect that the reason to use it is that the cans and the associated empty space is cheaper than actually having solid concrete (and may be partly necessary to reduce the weight of the concrete and thus associated stresses with it). You're probably (mostly) correct. For beams, reducing the weight of the beam itself will reduce stresses in the beam and ...

9

The reason is that you assumed that the elements around node $\text{D}$ will be the first to fail. That is not the case. Indeed, it is the elements under compression ($\text{AB}$ and $\text{BC}$) that will fail first. Also, you assumed that all the members around $\text{D}$ will present the same axial force, which is untrue. To see this, here's your ...

9

Bollards and other defensive oriented structures significantly predate the 2016 Nice attacks. They have been in place at the construction of many buildings in the US and across the world for decades including government and multi-national corporation buildings. You probably just never noticed them. It is my opinion that you see more of the type above due ...

8

Multi-way bridges are rare for river crossings for the reasons you describe; however, they are seen as a component of highway interchanges, usually when left entrances/exits are present or access ramps have been "braided" into an existing system interchange, or where a SPUI has been built over an existing divided highway. Viaducts over railroad tracks or ...

8

Meet Vladimir Shukhov, a Russian architect who first developed hyperboloid structures. He was born in 1853, died in 1939, and created over 200 hyperboloid structures in the intervening years. He was the reason hyperboloids gained the popularity that they did. His first design, the first hyperbolic structure ever, was the Shukhov Tower in Polibino, pictured ...

8

The weight of the gold would be about 52,110,000kg, over 900 meters square of floor area. This is about 82.4psi of floor pressure, or, under standard gravity, 57.9kN/m^2 live load. This is only an order of magnitude greater than typical industrial (storage, assembly) buildings that accept 7.5kN/m^2 across the floor surface. The total weight of the gold is ...

8

The dimensions of the beam and magnitude of the deflection are important here. In most structural applications, it's reasonable to assume the length of a beam is unchanged by a small deformation. One of the basic assumptions of beam theory is that there is some internal surface of the beam called the neutral axis that holds no tension or compression stress, ...

7

Assumptions The angle between the wall and the strut is $\theta$ $a$ is the depth of the table top $P$ is the weight on the table top, applied at the edge furthest from the wall The strut will fail when it buckles, which implies $F_{\text{max}}=\frac{\pi^2EI}{L^2}$ where $L$, $E$ and $I$ are the length, the elastic modulus, and the moment of area, ...

7

I am specifically thinking of a wooden beam... Wikipedia suggests I also need to know "Area moment of inertia of cross section" but I have no idea how to obtain this. If you're using standard wood dimensional lumber sizes, the American Wood Council (AWC) publishes a table of different sizes vs. section properties in the 2015 NDS Supplement, Section 3.1. ...

7

Depending on the region and structure of building the techniques might vary. Below are few suggestions Termite inspection is another popular method to determine the structure integrity of building. A handheld radar scanner from DeWalt might also do the job as describe here. Depending on the type of pipes a metal detector might be another good option. Non-...

7

You're hanging it from a rod supported by both ends - and need to use the bending equations. For this case (case 7 in the link), the max weight is: $$W_{max} = \frac{\pi d^3 \sigma}{8L}$$ $\sigma$ is the tensile stress, $L$ is the rod length, $d$ is the rod diameter. The sag is: $$\delta = \frac{4W_{max}L^3}{3E \pi d^4}$$ where $W_{max}$ is the weight, ...

6

Splitting a uniform load into separate pieces that are still continuous will have no effect. This is frequently done. As far as your question about bending in HE and EB, there shouldn't be any bending because all of the forces are balanced. A sum of the moments at H or E will show that the moments from the beams on either side are opposite and equal. That ...

6

why is it logical to have the position of shear center at the location of intersection of line of action of shear force and x axis? That statement isn't logical. I think you have misunderstood how the shear centre is defined. The shear centre is the point such that an applied force passing through the S.C. does not cause any rotation of the section. In ...

6

Can a typical mobile home support that much weight? No, most mobile homes are just flimsy wooden constructions where emphasis is on weight saving. If you want to stack cheap housing blocks I suggest stacking steel old shipping containers. They also come preequipped with anchor points in the corners. Can standard steel scaffolding provide enough support? ...

6

Adding to @Air's answer, there's also the issue of boundary conditions. A simple span where neither support allows for axial displacements will have a slight gain in length, including along the "neutral axis". This is because, in this case, the "neutral axis" will hold a tensile stress. Since the beam deforms, the neutral axis changes from a horizontal ...

6

Eurocode looks into this with very much detail, see the "Loading Standards" list, attached. You can see that there is a document dedicated to actions in silos and tanks. This deals with hydrostatic forces. But as a rule of thumb you have two types of loads: Self Weight (Dead Load): Loads that are fixed and do not change during the lifespan of the structure....

6

What chapter/section of AISC codifies this kind of problem? If you're looking for a specific code provision for this exact type of weld, you're out of luck. However, it is possible to solve this problem using basic mechanics of materials principles. For this case, I'm going to use elastic design. You could also use the instantaneous center of rotation (...

6

The column top holds some narrow thunk and that thunk holds the driveway floor. I think we have some nomenclature that needs to be cleared up here. What I believe you're calling a "thunk" is actually a bearing plate. This is a little steel platform that transfers the load from the bridge to the column. (source) The expanded portion at the top of the ...

6

Use an RHS over an SHS when you want significantly more bending/shear capacity about/in one axis than the other. The additional depth that an RHS has in one axis gives it greater shear capacity in this axis, and greater moment capacity about the perpendicular axis.

6

For impact force calculations you need some more information such as the shear modules and the material properties like toughness and tensile yield and shear yield. Also you need to define a physical object that will impact the sheet. If the object is much more rigid than the sheet and pointed it will go through like a bullet. Imagine an impact force has ...

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