Steel I Beam Load Capacity Chart
The following table shows the maximum allowable load (weight) a steel beam can support. This is based on the most recent research done by the National Institute of Standards and Technology (NIST). NIST has been conducting tests since the 1970’s to determine what type of beams are safe for use in buildings. These tests have shown that there is no significant difference between structural members made from different materials, such as concrete, masonry or steel. All three types of building components are designed to withstand the same amount of force.
The only difference is the strength of the material used to build them.
Table 1: Steel I Beam Load Capacity Chart
Load Capacity (pounds) Maximum Allowable Weight (lbs.) 0% Grade 60 Grade 70 10% Grade 60 Grade 70 20% Grade 60 Grade 70 30% Grade 60 40″ x 12″ x 8″ 6,000 7,500 9,800 13,600 16″ x 24″ x 8″ 5,200 6,900 11,400 14,100 19″ x 36″ x 8″ 3,700 4,300 10,600 17,800 25″ x 48″ x 8″ 2,500 3,200 9,100 21,000 33.5’x45’x8″-12″ 1.750 2.150 7.550 18.350 32.
x 24″ x 12″ 5,200 7,100 11,300 14,400 18″ x 36″ x 12″ 3,900 6,700 9,100 13,600 22″ x 48″ x 12″ 2,950 6,350 8,050 12,650 26.5’x48’x12” 1.865 4.750 5.250 10.550 32.25’x48’x24” 1.450 3.150 3.5’x58.5’x8″ 1.350 1.700 6.800 15.400
This chart can be used to determine the maximum weight on any floor of your structure if you know the size and shape of the floor (in this case an 8″ I-beam or a 12″ wide I-beam). There are two columns in the above table that need explaining.700 8,600
How much weight can a wood beam hold?
The answer to this question is not as easy as you might think. This is due to the fact that there are many different types of wood, each with different properties. It all comes down to the physical and chemical makeup of each piece of lumber. The first is labeled “Grade” which refers to a grading system developed by the American Iron and Steel Institute. It is used to describe the yield strength of steel.
The higher the yield strength, the stronger the material. As an example, structural steel yields at 60,000 pounds per square inch (PSI), while rebar yields at 45,000 PSI. (There are different grades for each size and shape of steel beam). The strength of each piece is always changing. Even though you might get a very straight, knot free, and defect-free piece of lumber, it is still subject to the elements. Moisture, sunlight, and temperature can all weaken a piece of wood.
How much weight can a soft wood beam hold?
Soft wood is easier to work with than hardwood but it is not as strong. The second is the actual size and dimensions of the wood (in this case I-beam). The third is the actual dimensions and shape of your floor. In my story, the beam was 12″ wide and 24″ deep. Yours could be different.
The fourth factor is load intensity, which is defined as the actual weight placed on an object divided by the area supporting that weight. Given a choice between a piece of soft wood and a piece of hardwood, always chose hardwood. The strength of soft wood is only half that of hardwood. You must also remember that the strength decrease is not in a linear fashion (as is the case with hardwoods), but in an inverse exponential fashion. What this means is that at 1/3 its original strength, the soft wood only needs 1/17th (or about 5%) more additional weakening before it fails completely. This ratio is expressed as a percentage, or in our example (from above), 600 lbs/12″=50% or 800 lbs/12″=66.7%. Both of these loads are below the maximum allowable load of 750 lbs/sq. Inch.
In my story, you will have noticed that the size and grade of the wood beam had a big effect on load capacity. So even a small decrease in strength can lead to a large decrease in safety.
At what point is your floor unsafe?
In my story, the floor held a maximum of 7,000 pounds. For an 8″ wide by 24″ deep I-beam, the “Grade” column shows a maximum allowable weight of 7,500 pounds. This is mainly because wood beams are shaped in an “I” or “H” pattern, and in my story the beam was a full 12″ deep. In the real world, most beams are only half as deep. The deeper the beam, the stronger it is and therefore the more weight it can hold.
As you might have noticed, the load capacity increases exponentially (faster than in a linear fashion). This means that a piece of wood that is only 1″ If you multiply 7,500 by 12″, you get a maximum width of 90″. If my story was correct, the floor would have still held over 6,000 pounds if it had been a hardwood floor. As it turns out, the actual size and grade of wood beam used in this sorority house was an 84″ long x 12″ wide Red Oak I-beam that only had a yield strength of 3,300 PSI or Grade 68. wide has greater load bearing capacity than a piece 2″ wide. No wonder the “I” beams that hold up large buildings are only 2″ by 4″.
The “Depth” column is the most important one. As you can see, the deeper the beam, the stronger it is. This is because as you go deeper into the piece of wood, you are actually endangering fewer fibers and therefore putting less strain on them. In my story, the fact that the beam was 12″ This is smaller and weaker than the average hardwood beam. The hardwood beams sold for residential construction are closer to Grade 100, which have a yield strength of 5,000 PSI.
Even though the floor could only hold 7,000 pounds, it would have been safe if it had just supported three normal girls. Unfortunately, the floor broke under the weight of two obese girls…
Why didn’t the overweight pledges break through the floor?
Why didn’t they? deep was what made it strong enough to hold over 6,000 pounds. Red Oak has a Janka Hardness of 1,290 lbf and a Specific Gravity of 0.60.
How does your floor compare to a bridge?
Bridge – How much does it weigh?
In my story, the bridge held up at least 3 cars before collapsing; this is what we refer to as the Dead Load. Think about it.
In my story, the floor broke under the weight of two girls that were 500 pounds EACH. If a floor can only hold up three normal girls, why did it hold up four times that weight?
One thing you learned in this class is NEVER trust your intuition. Intuition fails more often than you think, and this problem is a perfect example. Most people think that when you add more weight on a structure, it gets weaker. The two main factors contributing to this load are the actual weight of the bridge and the weight of the cars driving over it, or in other words, the live load. As a general rule, the heavier the bridge, and the higher the traffic, the stronger the bridge needs to be.
To find out how much a bridge weighs, we need to add up all of its components. As a frame of reference, let’s use the Green Bridge in Washington State. This is not true; the structure gets stronger. This is because when force is applied to an object (in this case weight), it has to be absorbed by the supporting material. If you double the weight, you double the force, and the amount of force that the supporting material has to absorb doubles as well. So if your intuition was right, then a floor that holds three normal girls would break when one more girl stepped on it. Fortunately for humanity, intuition fails us on this one.
As it turns out, the bridge that collapsed had a deck, stringers, intermediate beams, and two sets of suspender cables (which attach to the top of the short columns). The first set of cables attached to the ends of the columns were for the street car and no longer exist. Each end also had guardrails. The weight was distributed between the three spans and each pier where the columns were.
When you drive on a bridge, your car is putting more than just its own weight onto the bridge; it’s also putting the weight of the car itself onto it. The amount of force that your car is exerting onto the bridge when driving over it we refer to as the Live Load. In the case of the Green Bridge, there are about 10,000 cars per day driving over it at about 12.5mph.
The columns were made of solid rock, and concrete was used for the bases of the columns and the tops of the pier columns. On top of this was a steel cap to prevent damage to vehicles.
So what does all this mean? It means the bridge weighed a lot more than you might think. Did it actually weigh over 1 million pounds? Most definitely not. That is the dead load weight. The actual weight of the bridge would have been much lower due to everything being hollow. That’s a total of about 625,000 pounds of live load.
Now remember, the bridge itself is about 1,086,000 pounds, so it needs to be able to handle about 526,000 pounds more than its own weight.
The Green Bridge in Washington (not that one!) has a deck span of 150 feet and total length of 605 feet with an asphalt surface. Let’s see how much it weighs. Also, the dead load weight does not account for the counterweight of any of the cars driving on it.
The North Bay Bridge (the old bridge) had a similar dead load weight. That bridge actually weighed much less than 1 million pounds. This is why the new bridge only needed to be wider rather than longer. The width was increased to 75 feet while the length stayed at 2000 feet.
The bridge in question has a span of 200 feet and a total length of 525 feet with an asphalt surface. Let’s see how much it weighs now.
A key focus in the design of any bridge is keeping the dead load weight down. This means less piers, which means less expensive. This also means a cheaper bridge to maintain and less weight for its own supports to hold up. The Green Bridge actually had the same length and number of spans (except for the new one) as the old bridge, but it only weighed about half as much. This is why it could be built for only $5 million.
The dead load weight is just under 1.1 million pounds. This means that any vehicles driving on it add about 550,000 pounds to the total weight.
That’s a massive bridge!
In both cases, don’t forget that the actual weight of the bridge is much less than the dead load weight. I’m not sure what the exact figures are for either bridge and I don’t care to find out because they’re so specific that they aren’t important in this discussion.
The point being that the bridge is not going to break if two cars pass on it at the same time. The bridge can easily support 10,000 times their combined weight (500,000 ÷ 2 = 250,000; 500,000 + 250,000 = 750,000; 1000 kg ÷ 750 = 1.33333333333333), even when factoring in the dead load weight. What IS important is that each bridge can handle its own weight plus about 550,000 pounds of weight on it.
The Green Bridge has a 15 foot wide lane, a 6 foot asphalt buffer on either side, a 4 foot wide sidewalk on either side and 6-8 feet of clearance under the deck. That means there’s 21 feet from one side to the other and the deck is about 16 feet above the water.
Now we come to the really cool part. There are tricks that bridge builders use to prevent things like this from happening.
The new bridge uses a design called a “truss”. The top portion is a triangle, which is the basis for the word itself. A triangle is actually stronger than a rectangle because the lengths of the sides are always being subtracted from each other. By using triangles, you don’t have to worry about supporting the bridges’ own weight because they all point downward. Let’s pretend it’s a little deeper than it actually is (40 feet or 12.2 meters) just to be safe.
The North Bay Bridge has 15 foot lanes and 12 foot outside shoulders on each side. It also has a 10 foot wide walkway on the outside (connected to the deck) and a 5 foot sidewalk on either side of that. That’s at least 31 feet from one side to the other with the deck being 16 feet above the water.
As long as the walkway and the outside shoulders stay outside of the towers’ “effective” span, they don’t have to be factored in. In other words, as far as the bridge is concerned, those don’t exist because the dead load weight of the bridge isn’t factored into that total either.
The effective span is an imaginary line between the two actual towers. Anything outside of that doesn’t count. Why would it? It’s outside the towers!
This gives us a difference of 1.5 feet (31 – 30.5 = 0.5, 0.5 X 12 = 6).
We’ll use that as our constant to adjust for the gap between the lanes and shoulders.
Since we can’t subtract a negative number, we’ll need to flip it around, thus making it a positive number. This means that we’ll have to subtract 1. The width of the bridge is, of course, factored in because you don’t want it to fall on its side.
The Green Bridge already had a tremendous amount of clearance under it. The North Bay Bridge has 16 feet from the deck to the water when there’s no current. That’s without any allowances for sidewalks or shoulders. This gives a lot of room for error.
But what about when the walkway and outside shoulders on the North Bay Bridge are factored in?
Sources & references used in this article: