Trickle Down Arch Design

Our latest design challenge is a brick arch with recessed accent courses that tie in to the recessed accent courses of the running bond of the building.  Here is a building in Baltimore with a similar style arch.

What complicates the matter further is the 32" soffitt and the question of how we will prefabricate the arch.  When designing a normal radial brick arch the measurements that we need to determine are the circumference, angle, length of the outside arc, and brick size.  

circumference x angle  =  length

360    

But in this case the masonry opening arc is half round and the outside arc is elliptical.  Also we are limited by the size of brick because the joints of the accent course must line up with the running bond.  Here is where it gets tricky.  Instead of starting with the arch, I started with the running bond and accent course, and started at the top of the arch.  To pass the eye test the arch cannot be too tall in the center, but also the 2 1/4" brick size must line up to the same number of courses in the arch.  The only way to get the desired effect was to start with 3 5/8" closure size brick towards the top of the arch, then work our way smaller towards the bottom.  This is how we came up with the ellipse.

I am no math wiz, so if anyone knows a better way to reverse engineer this thing send me a message.  What has me mixed up is the length of the elliptical arc combined with the size limit of the radial segments.  

Prefabrication: material cost vs. labor cost

    I was trying to come up with a formula for masonry contractors of how to quantify in dollars how utilizing prefabricated brick arches saves money.  Like a profit & loss statement there are fixed numbers and numbers that can manipulated.  We are doing a job right now for LFJ masonry called Watkins MOB in Virginia.  We have prefabricated and delivered 86 brick arches.  Eusebio Cantone of LFJ told me that when they estimated the project they added the price of the arches to the material costs and subtracted estimated production time in hours from their take-off.  He said:

     "The largest benefit is that we can set these and keep going, we don't have to wait! At the end of the day you can figure the total time you took to fabricate the arches (man-hours) and that would be your time savings on the project. Based on crew size and number of arches on the project you could also determine the following, the project saved X number of man-hours to fabricate and set arches therefore saving X number of days on the total project and that is where equipment savings comes in as well."

I figured we used 8 diamond blades, cut over 8000 brick, purchased, cut and bent 3500 feet of #4 epoxy coated rebar, 20 boxes of wall ties, and purchased and mixed 800 bags of cement/grout.  We also dedicated 2 employees to work on this project for 100 days each.  This does not take into account utilities, fuel, transportation, and maintenance.  Other costs that are sometimes overlooked by contractors that are reduced by installing prefabricated arches are rental equipment, employee insurance and liability.

So here is the math that gives you more profit:

$ INCOME

- $ ARCHWAY SYSTEM PREFAB

= X

+ $ SAVED IN LABOR HOURS 

+ PRODUCTIVITY ( $ FROM DAYS ON SITE)

+ MATERIAL NOT PURCHASED (REBAR, CEMENT, WALL TIES, ETC.)

+ EMPLOYEE LIABILITY

+ EFFICIENCY (ON TIME DELIVERY, START THE NEXT JOB SOONER)

+ RENTAL COSTS AND MAINTENANCE FEES SAVED

= MORE $$$$$$$$$$$

The hardest thing to put into the equation is efficiency...lets say LFJ masonry finished this project 20 work days ahead of schedule, how do we add a dollar amount to the equation.  In reality that same masonry crew can complete more jobs in a given year, therefore increasing revenue.  I think efficiency would be a % that carries over to the revenue for the year on the profit/loss statement.  

Thanks Seb.  When I take some pictures of the finished buildings I will be sure to post them.