Construction Employment Increases in 39 US States Year-on-year and 34 States from June to July
Construction firms added jobs in 39 states from July 2013 to July 2014 and in 34 states from June to July, according to an analysis today of Labor Department data by the Associated General Contractors of America.
Association officials said the employment gains are good news, but that the pipeline of skilled craft workers, supervisors and other employees appears to be emptying rapidly.
Ken Simonson, the association's Chief Economist, said: "The overall trend in construction employment has been very consistent in 2014, with more than three-fourths of states adding jobs each month on a year-over-year basis. However, growing numbers of contractors say they are having trouble finding skilled workers or subcontractors that can supply such workers."
Nevada experienced the largest percentage increase in construction employment between July 2013 and July 2014 (13.4 percent, 7,500 construction jobs), followed by Delaware (13.3 percent, 2,600 jobs) and Florida (11.1 percent, 40,600 jobs). Florida again led all states in the number of construction jobs added in the latest 12 months, followed by Texas (23,600 jobs, 3.8 percent) and California (22,600 jobs, 3.6 percent).
The District of Columbia and 11 states shed construction jobs during the past twelve months, with New Jersey again losing the highest percentage and total (-6.5 percent, -8,900 jobs). Other states that lost a high percentage of jobs include West Virginia (-5.8 percent, -2,000 jobs), Mississippi (-5.6 percent, -2,900 jobs) and Arizona (-4.8 percent, -5,900 jobs). Arizona lost the second-highest number of construction jobs during the year, followed by Mississippi, then West Virginia.
Delaware had the largest percentage gain (5.7 percent, 1,200 jobs) among the 34 states that added construction workers to payrolls between June and July. Other states adding large percentages of workers in the month included Alabama (4.9 percent, 3,800 jobs), Kentucky (3.4 percent, 2,200 jobs), New Mexico (3.1 percent, 1,200 jobs), and Virginia (2.6 percent, 4,700 jobs). Virginia added the most workers during the month, followed by Florida (4,400 jobs, 1.1 percent), Texas (4,000 jobs, 0.6 percent) and Alabama.
Fifteen states and DC lost construction jobs between June and July, while construction employment was unchanged in Rhode Island. California lost the most construction jobs during the month (-6,400 jobs, -1.0 percent). Other states with large monthly declines in total construction employment included New York (-3,500 jobs, -1.1 percent), Georgia (-1,500 jobs, -1.0 percent), Nebraska (-1,400 jobs, -3.0 percent) and Kansas (-1,100 jobs, -1.8 percent). Nebraska had the highest monthly percentage decline, followed by West Virginia (-1.8 percent, -600 jobs) and Kansas.
Association officials said it is encouraging that a large majority of states added construction jobs for the year and the month. However, they cautioned that construction firms in many parts of the country appear to be experiencing varying amounts of labour shortages. They said that while worker shortages appear most severe in fast-growing states like Colorado and Texas, there is still time for elected officials to act on the association's workforce development suggestions before shortages become more widespread.
"We are at real risk of going from a situation where firms couldn't hire because there wasn't enough demand to firms not being able to hire because there aren't enough qualified workers," said Stephen E. Sandherr, the association's Chief Executive Officer.
Why engineers must always consider human-induced vibration
Human induced vibration, or more accurately vibrations caused by human footfall, often conjures images of Millennium Bridge-style swaying or collapsing buildings.
But in reality, the ‘damage’ caused by human-induced vibrations is less likely to ruin a structure and more likely to cause discomfort in people. Though not as dramatic as a structural failure, any good engineer wants to make sure the people using their structures, be it bridges or buildings or anything in between, can do so safely and comfortably. This is why human-induced vibration must be considered within the design process.
Resonance v Impulse
There are two ways that human-induced vibrations affect structures: resonant, and impulse or transient response. Put simply, resonance occurs when Object A vibrates at the same natural frequency as Object B.
Object B resonates and begins to vibrate too. Think singing to break a wine glass! Although the person singing isn’t touching the glass, the vibrations of their voice are resonating with the glass’s natural frequency, causing this vibration to get stronger and stronger and eventually, break the glass. In the case of a structure, resonance occurs when the pedestrian’s feet land in time with the vibration.
On the other hand, impulse or transient vibration responses can be a problem on structures where its natural frequencies are too high for resonance to occur, such as where the structure is light or stiff. Here the discomfort is caused by the initial “bounce” of the structure caused by the footstep and is a concern on light or stiff structures.
Engineers must, of course, design to reduce the vibration effects caused by either impulse or resonance.
Potential impacts from human induced vibration
Human induced vibration can lead to a number of effects upon the structure and its users. These include:
- Interfering with sensitive equipment Depending on the building’s purpose, what it houses can be affected by the vibrations of people using the building. Universities and laboratories, for example, may have sensitive equipment whose accuracy and performance could be damaged by vibrations. Even in ordinary offices the footfall vibration can wobble computer screens, upsetting the workers.
- Swaying bridges One of the most famous examples of human-induced resonance impacting a structure occurred with the Millennium Bridge. As people walked across the bridge, the footsteps caused the bridge to sway, and everybody had to walk in time with the sway because it was difficult not to. Thankfully, this feedback can only occur with horizontal vibrations so building floors are safe from it, but footbridges need careful checking to prevent it.
- Human discomfort According to research, vibrations in buildings and structures can cause depression and even motion sickness in inhabitants. Tall buildings sway in the wind and footsteps can be felt, even subconsciously by the occupants. It has been argued that modern efficient designs featuring thinner floor slabs and wider spacing in column design mean that these new builds are not as effective at dampening vibrations as older buildings are.
- Jeopardising structural integrity The build-up of constant vibrations on a structure can, eventually, lead to structural integrity being compromised. A worse-case scenario would be the complete collapse of the structure and is the reason some bridges insist that marching troops break step before crossing. Crowds jumping in time to music or in response to a goal in a stadium are also dynamic loads that might damage an under-designed structure.
How to avoid it
As mentioned, modern designs that favour thinner slabs and wider column spacing are particularly susceptible to all forms of vibration, human-induced or otherwise, but short spans can also suffer due to their low mass. Using sophisticated structural engineering software is an effective method for engineers to test for and mitigate footfall and other vibrations at the design stage.