Is this a feasible structure? Please share!

[dymobs]

Hi All,

I am a licensed PE in the state of Texas, but not structural or civil. I am reaching out to get your opinions on a structure planned in my neighborhood. This is 100% personal curiosity, and has nothing to do with my work (oil and gas). My gut feel is that it is a bad idea, but I would appreciate your feedback to my concern.

I live in a quiet area in Houston, TX. Most of our homes are 1-2 stories. A developer bought a small piece of land that used to hold two homes and wishes to put a nine story building on it. Details:

Land: 100' x 135', 13,500 square feet, 1/3 acre

Structure:

- 9 levels: bottom 2 for parking, top 7 for condos

- Parking structure will start 5' below ground level. The two levels will be required to hold 32 cars total.

- Footprint ~ 90' x 125'. They are building ~5' away from property line, for sidewalks and city regulation.

- Height will go from 5' below ground to ~ 90'+ above ground.

Materials: Concrete and metal (steel). Not a wood structure.

Developer: has only built townhomes and single family homes. NO tall building experience.

Soil: No specifics, but softer/more moisture. Basements and underground parking is very, very rare in Texas because of softer soil and being prone to flooding.

Neighbors: Neighbors have older structures on concrete slab foundations 10' from the propety line. Therefor, their distance from this large structure will be 15' or so.

Precedent: The tallest building in the area is 55' currently, but the foundation is much larger. One two story building in the area has similar partially underground parking but it is known for flooding.

Questions:

- Cost? (haha, I figured I would ask). I estimate their projected total sales to be: $12.75 million

- The parking structure seems odd. With those outer dimensions, with structural pillars in the supporting throughout, will 32 cars be able to maneuver through the two levels of the parking garage?

- Neighbors: will their structure/foundations possibly be effected by this structure? it will be ~ 15' away.

My intuition tells me this is a difficult, expensive project. However, I may be wrong. Do you have any questions you think would be important to ask the developer, to make sure they are taking these things into consideration? I have attached their drawing of it. Note the parking garage extends beyond the living area a bit.



Thanks!

Diana

 

[blybrook PE]

To answer your first question, Yes, this building is feasible.

There are a couple taller hotels and other office structures in downtown Anchorage that sit on clays, sands and other liquifible soils. They are also well braced and detailed to prevent damage in a design earthquake, let alone tip over. One is a 5 or 6 foot thick mat foundation combined with piles and one other is ~70' piles, IIRC. If they can be built here to that kind of demand requirements, you'll have no problem in your neck of the woods, if done properly.

Now, to the meat of the matter, what are they doing for the foundation? With soft soils (likely clay from my limited TX experience), do they think a mat foundation will be sufficient, or are they going to utilize piles?

How are they going to mitigate excavation limits to prevent damage to neighboring structures if they are to overexcavate for the mat foundation? Am thinking about OSHA required side slope limits, a deep excavation will have potential to undermine neighboring foundations if not properly handled.

How are they going to mitigate potential vibration damage during pile driving if utilizing sheet pile walls or driven pile supports?

Construction laydown area seems non-existant. Are they going to shut down local roads, and if so, how will that affect surrounding residents? Have the neighbors had a chance to determine work hours for construction? Noise will likely be a matter to some if in a residential neighborhood.

The height of the building will likely shade nearby homes, not much can be done to mitigate that issue though. Will any homes loose sight lines or views worthwhile? Some people won't like to look out their windows and see a concrete wall (others like that though).

As to the parking garage, it could be done with a Post Tension concrete slab so that there are no interior columns. Just one option that could be on the table. We can't tell from the renderings one way or another. I've seen this style of construction elsewhere and it seems to work well enough.

Bottom line, you are correct, it will be an expensive endevor. If pulled off correctly, it could mean more business for the developer elsewhere. Hope this helps some. It's just a really quick overview of a few potential issues I see after a quick review of your post.

 

[dymobs]

Thanks so much for the feedback. These structural questions are exactly the type I want to ask the developer. Truthfully, we don’t want an 8.5 story building in the neighborhood but have no zoning. Given this project covers just two lots, if these developers with no mid/high rise experience succeed, my neighborhood could see many more in the near future.

We are extremely concerned about neighboring properties and, like you asked, would like to know exactly how they are going to mitigate damage to other structures. The perimeter of the building will be just 15’ from some 1970s townhomes, many of which are already starting to see some foundation settling. Neighbors will be getting a current-state structural analysis done prior to construction allowing them to establish if the developer causes damage to their property. A whole other issue is mature trees on neighboring lots that have substantial root systems extending into lot in question. Cutting 40-50% of their roots systems for the foundation will kill them for sure.

Lay down and parking areas have been a big concern that we have already brought up (unresolved). Some of the roads in the neighborhood are protected brick streets from the 1800s. The intersection in question is two roads with no parking allowed. One is single lane each way, the other is one way. An elementary school is a block away. They said once the parking garage is complete, workers can park in the parking garage as they build up. Given the ~5’ border of unused property, I foresee any cranes ultimately being in the road.

Partially underground anything in Houston floods. Always. I am sure they have a plan to prevent that, but I don’t understand why they would be the only developers to think of it if it is that simple.

Quality of life is another huge concern. You are correct regarding sunlight. Using basic shade studies we have shown that neighbors, some of whom have solar panels, will lose most of their sun. And breeze for that matter. Noise is a valid point, considering the estimated construction time is 18-24 months, this isn't a short term nuissance.

They could build ~$7mil townhomes with slab foundations and wood structure on this lot. They could likely heavily reuse engineering from a previous project, as they have built townhome developments before. This condo development will require all new engineering, make ~$12.5 million total revenue, have substantially higher construction costs, and be an uphill battle with our vocal community. While revenue may be more for the high rise, we hope to persuade them that townhomes will be better for everyone long term.

They say they are 3-5 months from applying for permits, so I am wondering if their engineering hasn't really been fleshed out so they are unaware of some costs. Maybe that is optimistic.

Thanks again. I really appreciate your thoughtful points and questions.

 

[engineergurl]

hijacking so a bacon butt displays

 

[knight1fox3]

Nope