Sites Map ACL Project List

Drayton Header
Drayton Hall Conditions Assessment

John on scaffold
Due to the difficulty of measuring cracks on the ceiling, each crack intersection point was mapped to the floor using a plumb bob.
The marks were then measured from two different established points on the floor allowinf for easy triangulation into a digital file.
Lindsay on floor
Included with this process was measuring the vertical shift of the ceiling using a laser  level, whihc helped to identify the low points on the surface.
What's So Important About What You Can See?
The visible surface of the ceiling is only a small part of the entire ceiling floor system.
It has been suggested that the variable sizes and patterns of existing cracks may be external indicators of different conditions of this entire ceiling/floor system, which include the construction and movement patterns of the joists above, the location of lathing fields, as well as the areas of delamination. 

Cracking and delamination may not always result from the same cause although crack size may be directly related to the areas of delamination.
While these cracks may indicate the location of problems with the ceiling/floor system, they also function in a positive way providing control joints which allow the non-flexible surface of plaster to bend with the moving system, helping to reduce the appearance of additional cracks. Unfortunately crack propagation is difficult to limit, and the continued growth of existing cracks may be unavoidable. Under force, an existing crack will continue to extend outward until it reaches a limiting edge. Additionally, under a constant load an existing crack will be more likely to continue to grow before new cracks appear.  
Concentrations of existing cracks are directly linked to the sizes of the cracks.
Smaller cracks may be closer together, each taking up some of the flex. Larger cracks may be taking the same amount of flex requiring fewer cracks to distribute the force. Areas of the ceiling, which have been compromised and repaired can directly impact the direction of smaller cracking but do not seem to have an impact on the larger cracks. Finally the patterns of the vertical deflection of these cracks also show areas where the ceiling has deflected the greatest under its own weight.

Capturing the Data
The initial efforts involved collecting data. Old information existed and was incorporated into the final set of maps. This early data consisted of a 1991 survey which was conducted using a traditional acoustic method of tapping on the surface of the plaster and listening to the ring. While this approach is important it is highly subjective. Additionally in this 1991 survey a map was created to identify the location of the cracking patterns, which was incorporated onto a rectified photograph of the ceiling. The final result, while good, lacked accuracy. New data was collected using a plumb bob and two known datum points. The intersection of each crack was identified and mapped in AutoCAD using X, Y coordinates based on the measurements taken from the datum points; additionally the Z coordinate was mapped from these points using a laser level which created a level datum line around the room. Once all of the data was collected and digitally drawn in AutoCAD, each condition was then imported into Arcview. From this point Arcview will be used to create regression modeling to identify the correlation between the crack patterns and their variables. Spatial analysis will be conducted using three extensions including Spatial Analyst,  3-D Analyst and Geostatistical Analyst in order to find the spatial structure of the cracks such as density as well as to create predictive maps to identify potential threats and risk to the ceiling.
 To view the images below in full screen mode, and to read the complete captions, click the small icon in the top right corner of the dark "viewer" screen.