For this project we were tasked with designing and constructing a fence system for a family’s backyard so that their son with autism and sensory needs can safely enjoy outside recreation without needing to be monitored at all times.
The family for whom this project was designed for has a high-school aged son with autism and sensory needs. The son has a tendency to roam and a fear of steps/platforms, so the family requested a fence for their backyard so their son could enjoy time outside without the need for constant supervision. In addition, the family also wanted a railing system with a small ramp for their front porch to make trips outside of the house easier for him. Our group (10a) worked on the fencing system, while a second group (10b) worked on the front porch additions. The fencing system had multiple design requirements, including being able to keep the son from roaming, having at least one gate to allow for a lawnmower and the family to easily enter the yard, and having privacy/safety features to help prevent neighborhood pets from entering the yard while their son is there. With these design requirements in mind, we took measurements of the yard and created 3 concept designs to choose from.
Research was done to help with brainstorming ideas for the fencing type, style, and material, as well as designs for the gate. Given the family did not want to use chain-link or wired fencing for safety concerns, alternate fencing types were found including wood panel fencing, which the family believed would work best for their area. Multiple gate types were found that could accommodate the design requirements, such as a double-swing gate or a sliding gate. Lastly, to help with design parameters, common fencing panel lengths were researched to allow for greater availability of materials and resources for constructing the project. The 3 most common fencing lengths are 4 ft, 6 ft, and 8ft, and that would be used to help optimize dimensions in concept sketches.
Initial concept made after taking rough measurements of yard area, taking note of important locations such as the neighbor’s fence, driveway patio, and house. Fence type was modeled as a wood panel-style fence, shown at bottom of sketch.
Refined concept sketch of design #1, reducing many dimensions to match multiples of 8ft, which is one of the most common standard lengths for most paneled fence types. This allows for a reduction in cost both due to the shortening of fence as well as the availability of fencing resources for construction. Key locations and dimensions were kept to keep within design requirements.
Our 3rd concept has the same reduced dimensions as concept 2, but the gate type differs. Besides a hinged gate, we could also do a sliding gate, either in 1 or 2 panels. This allows for some more versatility at the cost of extra hardware
Based on our preliminary decision matrix, concepts 1 and 2 had the same score. Both had lower costs while keeping the design intent in mind, while the main difference was the cost and versatility of the gate types. Concept 3 has a higher versatility in design since a sliding gate could allow for the addition of various mechanisms to open and close the gate, even with a controls system. Concept 2 has the advantage of being more simple and cost effective, while still allowing for some limited mechanisms for helping to open and close the gate. In the end, we chose to use the larger dimensions of Concept 1 along with the gate style of Concept 2. Our fence panels were designed to be 8 ft long with 3 2×6 lateral supports to which 6 ft dog-ear style fence panels would be attached.
Our selected fence and gate design contains the fence dimensions of concept design 1 along with the gate design seen in concept design 2. These were chosen to both fulfill the yard dimensions required by the family as well as offer an ease-of-use gate that would be versatile for both pedestrian and vehicle entry.
The fence was designed to be made in 8-foot sections, each containing 3 2×6 lateral boards and 24 6-foot-tall fencing slats. These sections would then be mounted on 4×4 posts at 8-foot intervals. The posts were designed to have an extra 21 inches on the bottom to be buried and concreted in the ground to allow for adequate support.
The gate was designed to be 12 feet long, in order to offer overlap in the gate opening in the fencing. The gate would be constructed out of a metal frame with 2×4 lateral braces for mounting the same 6-foot tall slats used in the fencing for consistency. The gate has 2 doors to span the 10 ft opening and is secured with a drop rod on one door such that both doors can be opened or just one depending on the required usage.
The primary concern for the wood paneling was damage sustained by wind. For this analysis, we assumed a 40 mph wind force (approximately 4 lbs per square foot) across an entire 6ft x 8ft panel of the fencing. This results in a 196.8 lb force on the panel, which was converted to 875 Pa for analysis.
The analysis model distributed the 875 Pa force across the panel, with the 4×4 posts fixed at the bottom. With this, the maximum stress seen was 5.416 MPa. Assuming the yield strength of southern yellow pine to be 41.4 MPa (matweb.com), this yields a factor of safety of 7.57 for a 40 mph wind force.
With such a high factor of safety, it is safe to assume the design will meet the specifications even considering wood variation or other issues.
The construction of the fence involved 6 main phases: material delivery, post setting, lateral installation, slat installation, gate installation, and finishing.
1. The material delivery phase involved coordinating with the ME department and Lowes primarily to order all of the wood and hardware required for the project and delivering it to the site.
2. The post-setting phase involved marking the outline of the fence, setting corner posts, installing guidelines from corner to corner, and setting all of the posts in between to make the 8-foot sections. Some of the posts were set around 5-6 feet as necessary since the dimensions are not multiples of 8. The posts holes were dug using post-hole diggers and breaker bars, the 20-inch minimum depth was confirmed, then the posts were set using concrete while being held level and along the guidelines.
3. The lateral installation phase involved marking a consistent length on each post for all 3 of the lateral 2×6 boards, cutting the boards to length, and mounting the boards using decking screws.
4. The slat installation phase involved mounting the slats to the lateral boards along the entire fence length, using 1/8th inch spacing in between each slat. The slats were periodically checked for levelness to help ensure the fence remained as square as possible.
5. The gate installation phase included assembling the gate-frame kit, installing the 2×4 lateral supports, mounting the hinges, checking squareness, and attaching the slats to the exterior side of the gate.
6. The finishing phase involved cutting the tops of the posts off using a reciprocating saw to be as tall as the highest lateral boards firstly. Next, the fence and gate was stained using an electric spray-gun to efficiently cover the entire fence. The fence was inspected for any problem areas, the gate was verified to be secure and work as properly, and the project was completed with the family’s approval.
This was a very rewarding experience where our group had the opportunity to work together to work on this large-scale fencing project. We were able to improve our project management and teamwork skills to complete the fence and deliver a project that will help this family in need. We are very happy that we were able to help this family and give back to the community by putting engineering skills into practice.
