An Engineering Comparison of Post and Lintel Construction Method to Roman Arch Construction Method.

Presented by:

Autographs will be provided at a later date.

Ryan Barzee Alma Oliphant

Background Information:

The challenge in “span” construction is to create a structure strong enough to cover large distances while being able to bear heavy loads and not fall under its own weight.

The beautiful Roman bridge over the river Tagus at Alcanara in Spain.

The Collosseum, Built 81-96 A.D. (Rome, Italy.)

When a flat piece of stone is used to span a distance between two upright supports, the method is called post and lintel construction.

One problem with post and lintel construction is that excessive weight on the middle of the span may stress the stone and cause fracture or failure.

Temple of Olympian Zeus. Completed by the Roman Emperor Hadrian (A.D. 76-138) Columns are 6 ft. 4 in. diameter, 56 ft. high, 18 ft. centers. The beam span is obviously limited by the self-weight and the strength of the stone. Note the cracked span. (Athens, Greece)

The other problem with post and lintel designs is the difficulty of finding and transporting stone that will span large distances.

Stonehenge, England. Used here as an example, this is one of the earliest examples of post and lintel construction, 2000 B.C. The picture shows part of a 30-meter circle of 30 upright stones, each weighing about 25 tons, topped by a ring of 30 lintel stones, each weighing about 7 tons.

There are several modes of stress a span may experience. Some directly vertical, and some not as vertical.

Here the yellow diagram represents vertical loading conditions on the lintel members. Here the yellow diagram

represents horizontal loading conditions on the lintel members.

The Romans borrowed (and improved on) an idea from the Etruscans to combat the difficulties of the post and lintel method on construction.

Pont-du-Gard. Roman aqueduct built in 19 B.C. (Near Remoulins, France)

Railroad bridge (1909 A.D.) over the Landwasser Gorge. (Wiesen, Switzerland.)

Arch bridge 1757-1834 A.D. (Dunkeld, Scotland)

This idea, The Arch, later became the mark of Roman architecture, and a large influence in modern “span” construction.

Pont-du-Gard. Roman aqueduct built in 19 B.C. (Near Remoulins, France)

Railroad bridge (1909 A.D.) over the Landwasser Gorge. (Wiesen, Switzerland.)

Arch bridge 1757-1834 A.D. (Dunkeld, Scotland)

The Project:

The focus of this project was to compare strength of the Post and Lintel to the Roman Arch. The most prevalent strength being the vertical loading capability of each.

The Parthenon. 438 B.C. (Athens, Greece) Pont-du-Gard. Roman

aqueduct built in 19 B.C. (Near Remoulins, France)

STEP ONE: Model the two architectural designs in a computer drafting program. Catia was chosen to utilize it’s stress analysis capability.

The Post and LintelThe Roman Arch

STEP TWO: After the modeling was completed, a stress analysis was run to search for stress concentrations.

The Post and Lintel The Roman Arch

STEP TWO: This stress analysis was not used to determine actual loading capability, but rather to search for pockets of stress concentration.

The Post and Lintel The Roman Arch

STEP TWO: Actual load capacity was tested physically with scale models. This testing will be discussed later.

The Post and Lintel The Roman Arch

STEP TWO: A discussion of the computer analysis:

It is good to note a few details from this analysis. The above colors represent different stress concentration levels. The blue represents low concentrations of stress, and the red represents high concentrations of stress. Thus, the red areas denote possible failure zones under peak loading conditions.

STEP TWO: A discussion of the computer analysis:

In the Post and Lintel design, most of the stress (the red area), is located in the lintel member. This stress concentration acts as a focal point of the loading conditions, and causes fracture and failure to occur at that location. Note that the feet of the posts are not stressed compared to the horizontal member.

STEP TWO: A discussion of the computer analysis:

In the Arch design, the stress concentrations are distributed throughout the arch. Notice that the arch distributed the load down through the feet, therefore showing capability of handling more load than the Post and Lintel.

STEP THREE: Create physical models to be tested for loading capacity and stress concentration.

The Crabtree Technology building houses a computer controlled water jet cutter capable of cleanly cutting a block of steel several inches thick. To manufacture a testable model similar to an actual application of the post and lintel and arch designs, a block of concrete was profiled into solid post and lintel and arch models. A solid model was used to simulate blocks mortared together in an arch or post and lintel design. Concrete was used to simulate the stone utilized by the ancient Romans.

STEP THREE: Create physical models to be tested for loading capacity and stress concentration.

Several copies of each model were manufactured to allow for human error and varying material properties. Height, span, width, and thickness dimensions were kept identical to facilitate loading and failure data comparison.

STEP FOUR: Load the models to failure.

An Instron machine (like the one above) was used to test the models for failure load capacity and stress concentrations. Each of the models was installed and loaded to failure.

STEP FIVE: Analyze the data.

This is a comparison plot of averaged data recorded during several loading tests. The peaks in each of the lines represent failure. Notice that the model Arch held about 80 lbs of load before failure, 2 ½ times the Post and Lintel model that held just over 30 lbs before failure.

A Model Comparison of Post and Lintel to Roman Arch

0102030405060708090

0 0.05 0.1 0.15

Displacement (inches)

Lo

ad (

lbs)

Roman Arch Model

Post and Lintel Model

Conclusions:

Conclusion #1:

It may have seemed trivial, but the Arch is indeed a great improvement over the Post and Lintel. The Arch can span larger distances, and carry greater loads.

Conclusion #2:

As predicted by the computer analysis, the Arch distributed the load throughout the material, and therefore held a greater load than the Post and Lintel that focused the stress in one area.

Conclusion #3:

An Arch span will accommodate about 2 ½ times the load that a Post and Lintel, provided the span is not too great for the Post and Lintel.

Conclusions:

Arches and Domes in Churches and Mosques. http://www.brantacan.co.uk/gloscatharch.htm. November, 15, 2000. Internal Force Diagrams. http://www.arch.virginia.edu/~km6e/arch324/content/lectures/lec-05/pres.html. November 17, 2000. Romanesque Architecture. http://www.greatbuildings.com/types/styles/romansesque.html. November 25, 2000. Roman Bridges and Bridge Building. http://myron.sjsu.edu/ROMEWEB/ENGINEER/art2.htm. November, 15 2000. Sacred Geometry. http://www.geomancy.org/sacred_g/sacgeo-1.html. November 15, 2000. Structural Engineering Slide Library. http://www.eerc.berkeley.edu/cgi-bin/browse_godden?group=GoddenB2-13. November, 17, 2000.

Works Cited: