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Questions tagged [concrete]

For questions about the material concrete, or its application in an engineering context. Concrete is a composite material composed mainly of water, aggregate, and cement.

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1 answer
90 views

Is there a substance i could treat concrete with to make it not scratched by steel?

Is there a substance i could use that would harden the surface of concrete enough to make it resist scratching by steel?
0 votes
1 answer
547 views

Live and dead loads on lift core (passenger and cargo)

According to Eurocode or even better - JUS standards (if there is someone from EX-JU countries here), what are the dead and live load values and schemes for reinforced concrete lift core for both ...
1 vote
1 answer
51 views

How to determine the resistance provided by cement mortar?

I am attaching a steel rail and post guardrail to the coping of an existing parapet. The actions produced by the guardrail on the coping incur at point A as shown below. However, how do I find out if ...
1 vote
1 answer
50 views

Pumping water from under concrete slab basement

I have this situation, and wanted someone's opinion. Info: Concrete foundation basement, slab floor Weeping tiles and a sump pump is present / operational The house is near a pond. Grading is alright,...
1 vote
2 answers
214 views

Reinforced mesh at different distance in a concrete slab?

Trying to determine some information regarding the reinforced concrete slabs (reinforced with mesh) in an apartment, by looking through the holes in the middle of the rooms for lights, I've come ...
0 votes
2 answers
107 views

Is there a standard formula available to calculate lateral concrete pressure from the measurements of lateral concrete strain?

As shown in the image, I have done a vibrating wire type strain gauge and pressure cell (not shown in the image) instrumentation on full scale form. the objective is to measure the lateral pressure of ...
3 votes
2 answers
374 views

Once stopped, is it possible to achieve full cement hydration?

Several sources state that if hydration is stopped during cement curing, is not possible to resume it, and final strength will be compromised. But so far, I haven't found a reliable explanation. I ...
0 votes
0 answers
7 views

Concrete curling not ground slab

Hi I live on a first floor apartment I can feel some waves in my concrete floor I do not know if this poses any issues as it is not a ground floor slab
0 votes
0 answers
15 views

What does "dc" stand for in this Positive Bending Moment for Plastic resistance of a composite concrete slab formula?

I'm designing a building with a composite slab with profile sheeting and steel structure, while trying to test the resistance of the composite slab in "composite phase" to bending moment I ...
0 votes
0 answers
19 views

Ando dots or holes in concrete walls

I am making a concrete poured wall with holes where the bars to support the wood frame remain. Question is with plywood supporting frame what is the greatest distance between bars that will still ...
0 votes
2 answers
376 views

Modeling of a strap beam/foundation tie beam

The purpose of a strap beam (or tie beam - i'm not sure of the exact expression on english) as far as I know, is to enable foundation (horizontal) stifness. So my question is: how to model them ...
0 votes
1 answer
193 views

How bad is it if water is leaking through concrete in the lower parking levels of my apartment building?

I live in a 14 story apartment complex built in the 70s that has three underground parking levels. Today it looks like there's water leaking through cracks in the concrete on the second and third ...
0 votes
0 answers
15 views

Strut-and-tie models for concrete corbel cracking

I'm interested in how to perform serviceability limit crack width checks for concrete connections. Common type of connection is a corbel connection, which I'm currently investigating. I found one ...
0 votes
1 answer
72 views

Rebar lap splice tail bend

Is it a thing to bend the tails of rebars in lap splice?
0 votes
1 answer
40 views

Residential Post Tension Slab Setup

Background: Residential single story post-tension slab approximately 2300 sq. ft. new construction. Contractor has installed formwork and laid out post tension cables. Contractor has "...
1 vote
1 answer
222 views

Are the compressive and tensile stresses in the beams always equal?

If we examine the $example-1$ of cantilever beam 1 above, there will be shear force $Ft$ and moment $M$ that will keep the beam in balance statically. However, when we examine the strength, that is, ...
2 votes
2 answers
19k views

What are the regular holes in poured concrete walls called?

These holes are caused by bars that are put through the frame before the concrete is poured and then clamped, so the mold can't swell outward. Is there a name for these holes though that is widely ...
0 votes
2 answers
39 views

Why there are two equations to calculate effective depth for concrete beams? Eurocode

Are these the same? if so, why there are two equations given? is there a specific purpose? like, combining the equations for the ease of calculation etc? Why there are two equations to calculate ...
3 votes
1 answer
183 views

Why is the frustum of a cone used to slump test of concrete and not a cylindrical tube?

While performing the slump test for knowing the workability of a concrete mix one uses a tube having the shape of frustum of a cone in order to conduct the test. Why is not a cylindrical tube used ...
0 votes
3 answers
346 views

How does Gypsum Concrete work?

When mixed with water how does gypsum act as a binder in creating concrete?
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0 answers
32 views

How to calculate the available anchorage length in reinforce concrete design?

Hello everyone I am taking a course on RC this semester and I am kinda bumped out by all of the terminology here. The main question I have is what is the difference between anchorage length and ...
0 votes
1 answer
24 views

Question about commercial mix concrete design

What should I do here? Drying the aggregates prior to mixing make sense to me but would it be costly?
0 votes
2 answers
465 views

What does$ Ast = N16 @ 175mm $centres means in designing reinforced concrete?

I have the following problem, which I already know the general steps into solving. My general approach is: calculate I cracked as we are already told that the section is cracked, and then finally use ...
0 votes
1 answer
107 views

Consequential differences between World Trade Center (1973-2001) with steel columns and concrete columns? [closed]

How long would the World Trade Center (1973-2001) have stood after the large commercial passenger aircraft impact if the columns had been made of concrete? The perimeter columns were steel according ...
1 vote
1 answer
47 views

XPS foam panel as decoupling membrane for concrete pour over existing concrete slab?

Mortared bricks have been removed from a 50-year-old 12' x 12' concrete slab patio, leaving a rough surface and exposing a curved crack in the concrete which is about six feet long. If small-diameter ...
2 votes
3 answers
171 views

Concrete Strut and tie- modeling: Why can a tie and a strut cross at a point without forming a node?

I'm reading this source about concrete strut and tie design. Here is a picture from the site: I'm curious, why isn't there a node at the point where the lower tie crosses the middle diagonal strut? ...
-1 votes
2 answers
49 views

Question on plastic limit theorems and reinforced concrete

The lower plastic limit theorem is stated in Wikipedia as follows: If an equilibrium distribution of stress can be found which balances the applied load and nowhere violates the yield criterion, the ...
0 votes
1 answer
144 views

Base Support for a Tree house

I am building a tree house in my backyard and it is going to be relatively simple. There are no parts that require drilling into the tree. The whole house is propped up by four 4x4 wood supports. I'm ...
7 votes
2 answers
424 views

What's the name and purpose of this specific shape of hollows in a reinforced concrete slab?

Below is a stack of reinforced concrete slabs with hollows (camera is positioned along the hollows' axis). Such slabs are used for floors - you build walls of the next floor, then lay such slabs such ...
0 votes
0 answers
27 views

Building Engineering - Lightning Conductor [duplicate]

I went on a new building, for installing many "details" before people relocating inside. On the roof, I saw a very intriguing things about lightning conductor : they are inside walls, packed ...
1 vote
5 answers
718 views

Reinforced concrete by steel, poor durability, why?

I've been reading up about reinforced concrete, as it is one if not the cheapest way how to build (with some solid foundation). I found out that it actually has quite poor durability (50-100 years or ...
1 vote
1 answer
190 views

installing swing hook before concrete is poured

I want to place a swing hooks in place before the concrete is poured so that , i dont have to drill a hole later. My contractor is not ready to make these bolts with TMT bars itself.. what kind of ...
0 votes
0 answers
162 views

where did the concrete splitting test calculated stress formulat come from?

In compression test of cylindrical concrete sample we get the normal stress easily by dividing failure force by sample cross section, but how we can explain the formulat used to determine tensile ...
0 votes
3 answers
149 views

Why we say prestressed concrete is "more efficient"?

In my class my teacher said that prestressed concrete is more efficient, and when asked why he talk because of the constructing process. I believe because you have no cracked section hence you can use ...
1 vote
5 answers
240 views

Exactly what makes steel-concrete composite beam better than pure steel?

A composite action beam may have a concrete section the top, carrying the compression load, and steel at the bottom, carrying tension. But I have always thought that concrete had lower strength for a ...
0 votes
1 answer
70 views

Are there any ways to know whether the element has failed under loading, while knowing only limited properties?

I opt to check whether a precast concrete wall (no reinforcements, only concrete) withstand both vertical and lateral loading condition but the only properties I know are the Young's Modulus, density, ...
2 votes
2 answers
750 views

How to calculate the required prestressed jacking pressure to apply to a pre-tension concrete beam?

How does the fabricant of prestressed pre-tensioned beams calculate the equivalent pressure in the hydraulic jack (in bars) to the design prestress force (in kN)? Are there factors to multiply like a ...
1 vote
1 answer
83 views

Jointed reinforced concrete tie-bar smoothness

We know that in Jointed Reinforced Concrete pavements we use dowels and tie bars. Why are dowel bars Smooth and tie bars are deformed? Dowels are used to transfer about 40% of the load from one slab ...
1 vote
2 answers
47 views

Where to place air, water and electric cables in a composite beam [closed]

If water, gas and electrical cables have to pass through three (3) openings provided in the cross section shown in Figure 2, with tangible and scientific arguments specify the adequate opening for ...
0 votes
2 answers
224 views

Creep coefficient over time

I came across 2 creep coefficient diagram. First one is from Eurocode, second one is from elsewhere. I think the second one make sense, As the time progress, the creep coefficient shall increase, ...
2 votes
2 answers
38 views

Small building basement foundation moisture: permeable vs impermeable

I understand that moisture is the enemy of interiors. I know that the standard basement foundation for a house-sized building uses moisture barriers on the outside of concrete retaining walls to ...
1 vote
2 answers
206 views

Dependency between load capacity for reinforced concrete slab and thickness

How does the load capacity for a reinforced concrete slab depend on the thickness of the slab? Example: Let's suppose that we have the following constants: concrete quality (including the maximum ...
2 votes
1 answer
143 views

Are concrete screws suitable for repeated removal and reinstallation?

Is a concrete screw like the HILTI HUS3 removable? I.e. can it be repeatedly unscrewed and reinstalled as required? Will this damage the fixing or the hole in the concrete? We're thinking about using ...
1 vote
4 answers
6k views

Why does a beam in shear crack at 45 degrees?

Why does a beam in shear like in this picture crack at 45 degrees instead of vertically? This is called "Punching shear", and requires concrete reinforcement at an angle: Assuming that the ...
11 votes
2 answers
1k views

Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?

It is stated on here that: Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion ...
6 votes
3 answers
3k views

Concrete formwork - best approach to counter uplift forces, for a freestanding pour?

I'm casting a 4m long triangular-profile reinforced gravity retaining wall against soil movement due to a 1 metre jump in ground level. The lateral forces and moments on the formwork have been easy ...
0 votes
2 answers
78 views

Can anyone help me with the concept of bearing stresses in steel reinforcement in Reinforced Concrete?

When there is tension reinforcement(steel) embedded in concrete, does it not also undergo bearing stresses on account of the weight of the concrete and other forces which are acting above the steel? ...
0 votes
1 answer
71 views

How do extra building levels affect the foundation design apart for the extra load?

I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just ...
5 votes
2 answers
549 views

How much does the elasticity (Young's Modulus) of concrete and asphalt change with ambient temperature?

I'm assuming here that all materials will have a change in elasticity due to thermal expansion/contraction and a resultant reduction/increase in the strength of the bonds of the atoms leading to a ...
2 votes
1 answer
158 views

What's the difference between Creep and Dynamic Viscous Damping?

What's the mechanism behind each phenomenon and what's the difference between them? Why is Creep considered in the Constitutive Equation (taken as an inelastic strain) while damping is considered in ...