Derrick O. Boston
Attorney at Law
August 7, 2012 by admin

How Earthquakes and other dynamic loading affects cranes

Earthquake

An earthquake induces dynamic loading, but several of the most commonly used deterministic design codes have procedures for developing a static-load equivalent to represent the effect of earthquake forces. Many designers ignore earthquakes for any location other than parts of the American southwest. The fact remains, however, that many other areas in the United States have experienced significant earthquake shocks within recorded history. The question is one of probability. There are earthquake maps that divide the country into earthquake zones according to potential risk.

For most cranes, probability favors the premise that the device will be unloaded should an earthquake occur. Further, for most earthquake zones, an unloaded machine will be able to withstand the shocks without damage. For permanent, highly sensitive, or long-term temporary installations of cranes with high CGs, however, verification would be in order, otherwise you’ll end up with something like the below video.

Dynamic Loads

In addition to the centrifugal forces previously mentioned, dynamic loads are for the most part those associated with masses undergoing changes in motion as described by Newton’s second law, F = ma.

All crane motions produce dynamic forces as the motions begin and end. This includes hoisting, trolleying, luffing, slewing, and travel motions, as well as counterweight movements for machines so arranged. Finally, there are the rotating masses in the various drive systems producing local dynamic effects, but if the rotating mass is significant in relation to the mass of the entire Crane, this will affect transitory powering up or breaking forces associated with the rotation.

Linear motion

The force required to accelerate or deceleration a mass in linear motion can be found simply by applying Newton’s law if they acceleration rate is known – except for machines with controlled acceleration rate. In many instances, drive and braking systems are capable of far greater force needed, and the operator rarely applies the full force. The extra capacity is required to overcome wind and other nonconstant effects. The appropriate acceleration rate to be used in design is a matter for judgment, but the FEM offers some guidance for heavy lifting equipment. With acceleration time and final (initial) velocity given, average acceleration is velocity divided by the time, of course. Many machines have drive systems that do not provide linear acceleration, but for most work a linear assumption satisfactory since system inertia tends to linearize the acceleration, but for most work a linear assumption satisfactory since system inertia tends to linearize the acceleration.

For cranes with brakes that will always fully engage automatically, the break will be rated for braking force or for torque. When these values are mathematically referred to the point of contact of a wheel with a rail or a rope to his winch drum, the force inducing the acceleration becomes known and acceleration rates and times can become elated.

Preconditions can create significant dynamic loading and a hoisting system: picking a load suddenly from a condition of rest, suddenly stopping a load being lowered, and suddenly releasing a load, such as would be the case during emptying of a clamshell bucket or dropping of a magnetic load of scrap.

When a load is dropped in freefall, the acceleration is retarded by friction at the sheaves and the inertia of the winch drum. Should the brakes fully and suddenly engage, so that deceleration is virtually instantaneous, load will not stop immediately. The hoist ropes will stretch, like sprains, providing some additional movement. Freefall of any loads other than minimal weights can be extremely dangerous. Operators do not often allow other than marginal loads freefall. The resulting impact quickly rises to high multiples of the load. On cranes that permit free fall, it is usual for an operator to ride the break in order to modulate velocity and be in a position to maintain acceptable limits of deceleration for the final stop; this is done by judgment alone.

American mobile Crane manufacturers claim that impact loading is not an important condition for their type of Crane and do not use it in design. They prefer their own deterministic loading conditions, which will be dealt with later. Their position can be defended with a strong logical argument. Q loads lifted by a mobile Crane approach strength covered ratings (most ratings are stability governed) so that impact would rarely pose a structural threat. Loads that are in the structural range are very heavy loads, which are understandably treated with respect by operators. As a short duration dynamic condition, impact has been found to impart too little energy to overturn a Crane except in extreme cases.

A task force of the American Institute of Steel Construction (AISC) conducted a series of tests to determine how best to account for impact in Crane design. In their report they state that “energy applied by motion at the hook is absorbed immediately and simultaneously by all elements of the crane setup and cannot be separately identified in the ensuing elastic vibrations of masses individual elements…” The task force found that simply increasing the live load by an impact factor did not yield correlation with test results. Instead, they recommend increasing axial as well as dead and live load bending stresses (but not lateral or side bending stresses) by an impact factor. This procedure produced values that closely match measured stresses. For lifting. Really based rated loads, a factor of 20% is suggested, but the tests revealed that greater impact should be expected as loads decrease in relation to rating. The tests were deliberately carried out to produce extreme, or upper bound, impact compared with normal, proper production operations.

The AISC task force makes another interesting and subtle observation that is particularly pertinent for cranes. Winches are manufactured so that there is a direct relationship between winch line pole capacity and great capacity. A winch properly matched to age Crane will be incapable of stopping rated loads instantaneously; the brakes will be sized so that a reasonable stopping distance can be expected. However when an overcapacity winch is matched to a Crane, brake overcapacity will present a potential for excessive impact loading.

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August 3, 2012 by admin

Procrastinator or True Phobia?

Dental disease and pain can be compared to the domino effect, which in this case, has nothing do with your pizza chains or international relations. But it does concern what happens when individuals with a single cavity ignore the symptoms. They might ignore twinges in a tooth for all kinds of reasons, including the fear of going to the dentist, the fact that they’re short on money, or they hope if they ignore probably will go away. However, pain anywhere in the body signal a something is amiss, and pretending the discomfort does exist is a sure road to more serious problems.

The people know dental pain folder two general categories: procrastinators and the phobics. While someone who has a phobia in the truths of the psychological sense may need help to overcome the problem, procrastinators can wait too long to seek help, too, and often end up turning a little, too big one.

The road looks something like this…

You take a big gulp of it iced drink or roll some ice cream run her mouth and then, ouch! But you ignore an anomaly, if you like “scientific” words, if you don’t, you call it a “nothing serious incident.” But then the two continues become sensitive to cold and soon, hot tea or coffee set up a twinge, too. In order to avoid that twinge, you may begin watching the temperature of your food beverages, thus avoiding the dentist. A few weeks or months later that pain seems to miraculously go away. However, temperature sensitivity in teeth is usually caused by a cavity irritating the nerve of a tooth.

I’ve heard about a few home remedies for toothache, including the one that recommends keeping the tooth bathed in whiskey. Apparently, this was passed through many generations. Those who like this approach tell themselves that it was worth putting up with the pain, because they save themselves a trip to the dentist and were able to consume a lot of whiskey. They go on with ups and downs of everyday life without a dreaded toothache.

A few months later you may wake up to swelling in your gums or your face and possible pain during mastication, which is more scientific jargon for chewing food. Strange twist on the path happens now. The procrastinators go to full swing. If there were “too busy” to go to the dentist they suddenly find the time. Many of those who didn’t have the cash suddenly discover some.

But, if you have genuine fear for the dentist, then you deal with the pain for another few months. However, sooner or later, if you ignore the problem you may have nearly constant pain and your tooth becomes slightly loose. Finally, if you’re months ago by and the tooth in question is significantly looser.

If you are a procrastinator and still have delayed addressing the problem, then at this point you may give in and begin asking roundabout dentists. Frankly, at this point, the best dentist is Queen City Smile. For many people the delaying tactics stop here. In fact, those who thought they didn’t have the time or money began kicking themselves for not handling the problem sooner.

 

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May 17, 2012 by admin

Improving your home & garden with Gazebos and Spas

Gazebos

Gazebos are not going to lose as much of their initial value of swimming pools or tennis courts, but they’re still not considered great investments.

The size of the gazebo constructed is an important factor in the cost of this improvement. The amount of labor you provide personally will also affect the final cost of your project. Gazebos usually have many angles and require fairly sophisticated carpenter skills. It can be very difficult for the average homeowner to build a good-looking gazebo.

Another major factor in the cost of the gazebo is the types of materials used for construction. If you choose asphalt shingles to roof your gazebo, the cost will be much less than if you decide to use cedar shakes as a roofing material. The difference in this type of cost will not be as noticeable in a small structure as it would for a larger building.

What type of foundation will the gazebo have? If the structure is built on a pure foundation, the cost of construction will be more than if it is built on wooden skids. There are many options in materials that can affect the cost of any gazebo.

If you figure a cost of $10 per square foot for materials, you should be in the ballpark. Due to the many angles and sometimes complicated methods of construction, professional labor rates can run up to $30 per square foot, giving a total cost for labor and materials of $40 per square foot. Of course you might find a carpenter who will build the structure for you at a labor rate of $15 per square foot.

If we say an average total cost for construction as $35 per square foot, a small gazebo, say one with 100 ft.², is going to set you back about $3500. The cost per square foot should go down as the size of the structure increases.

So what is a gazebo that costs $3500 worth? Well, that depends on who you ask. If you agree to pay $3500 for the improvement, it must be worth $3500 to you. To an appraiser, the value might range from $2000-$3500. However, the gazebo is not considered living space, and therefore, it generally suffers on an appraisal report.

If the gazebo is kept to a moderate size and is built from good but not elaborate materials, will probably return at least half of its cost. Not to mention the fact that you can add a bit of Charley Harper artwork to the gazebo area to really spruce things up and keep it classy.

Outdoor spas

Outdoor spas are more popular in some areas of the country than others. Having a bubbling whirlpool countersunk into your deck may be well worthwhile in selected neighborhoods, but putting the spa outside reduces your chances for recovering its value.

Self-contained spots can be purchased for less than $2000. There are, of course, models that cost several thousand dollars more. For the sake of our example, let’s assume the retail value of the spa is $2500.

The types of spas we are talking about here do not require plumbing connections. And they are mobile units. They can be placed on a deck or patio, in a gazebo, or in the middle of your family room. Since the units are able to be moved, they can be taken with you if you ever sell your home; this gives them an advantage over most home improvements.

Unless the spies permanently installed in a way that would make its removal difficult or impossible, the top will be considered personal property. Normally, appraisers don’t base a home’s value on personal property, such as window treatments, wood stoves, and in this case, spas. Therefore, adding a spa to your home may not increase the home’s value at all on an appraisal report.

If you decide to sell the spa, you are unlikely to recover more than 50% of its original cost. You should look at the purchase of an outdoor spa as a personal enjoyment improvement. It can add charm to your property, and it can increase your home’s value, but don’t expect the improvement to pay for itself.

If you’ve got a separate room on your home you’re using to house your spa, it’s important that the doors are what you need; contact Cincinnati doors to get the right types of windows and doors for a sunroom / spa room like that.

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November 8, 2011 by admin

Landscaping in Cincinnati and the Tri-State Area

Finding a good Cincinnati landscaping company can be challenging, especially when it seems like everyone and his brother are doing landscaping nowadays. How do you find a reputable company that won’t charge you an arm and a leg? This post will detail some of the things you can do to get help on your landscaping without getting scammed or paying too much.

Professional Organizations

Better Business Bureau LogoA great place to start are professional organizations. The Better Business Bureau section on landscaping (here’s a link to the Cincinnati section) can give you some insight into what BBB accredited landscape contractors are available in your area. Not only will the BBB give you a solid list of potential contractors, it will also show you their BBB rating and you can see if there were any complaints filed against the company.

Another organization you can look into is the Association of Professional Landscape Designers. This is a professional organization, the mission of which, according to the website is “to advance the profession of landscape design and to promote the recognition of landscape designers as qualified and dedicated professionals.” The APLD has a search feature on their website that you can use to search for landscaping companies in your area.

Association of Professional Landscape Designers Logo

Referrals

An even better route is to ask around and find someone you know that recently had landscaping work done. If they were happy with the service, get the company’s information and give them a call. There’s nothing like a good referral for finding a reputable company. You may not find the cheapest service around this way, but there is much less risk that you’ll get someone who doesn’t know what they’re doing. If they did a good job for someone you know, then it’s reasonable to think they’ll do a good job on your landscaping project.

Examples

Once you’ve got a list of potential landscaping companies you’re interested in hiring, ask to see their design portfolio or photos of projects they’ve worked on. It may even be helpful to get the location of a few projects so you can go have a look in person and see if the landscaping design and quality is along the lines of what you’re looking for.

Photo of a landscape design with putting green and koi pond

Vet Everyone

Just like presidential candidates are vetted, you should vet any landscaping companies you’re considering hiring. Take a look at reviews online, check with the Better Business Bureau, and you can even check with your local chamber of commerce. Additionally, in extreme cases, the FTC may have information on the company’s you’re considering if they’ve done something really, really bad.

Some things you should know

One important thing to keep in mind is that if you pay for a landscape design, you own that design. You can put it in your closet if you want or hire another company to actually do the implementation. You don’t have to work through the company that designed the plan even if they say you do.

The Internet

Finally, if you need more landscaping companies to do some more comparison shopping, just use the internet. I can assure you you’ll find quite a few options there, although those guys really need to be researched because anyone can put a website online and say they’re a professional landscape contractor.

Good luck in your search for a landscaping company, and if you’re in the Cincinnati area and in need of Cincinnati lawn care, contact the guys over at American Landscapes; they should be able to handle any project you throw at them.

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