When it comes to enclosing large building volumes, it is hard to beat tilt-up concrete construction for economy and durability. Long considered the mainstay for warehouses and big-box retail, the tilt-up method is now frequently employed for commercial projects, churches, schools and Class A office buildings nationwide. With newer types of occupancies driving attention to aesthetics higher and higher, the importance of minimizing concrete cracking in the site-cast precast wall panels is greater than ever.
To successfully lift the panels for most of the tilt-up projects designed and built today, the use of sophisticated computer software to analyze the stresses generated in the panels during lifting is required. A specialty lifting engineer, often associated with the tilt-up accessory vendor, who has the required expertise and experience, most often provides this service. Typically, the panel designer will not provide the analysis and design required for lifting the panels. However a general understanding of the lift engineering process will help in designing panels that can be erected economically with minimum potential for cracking during construction.
chord pad crack
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Ideally, the tilt-up panels can be erected without developing any cracks during the lifting process. Therefore, the panels are typically designed using only the allowable flexural tension strength of the uncracked panel section without relying on the steel reinforcement. The calculated bending stresses within the panel are kept low enough so that cracking should not occur. The minimum concrete flexural strength required prior to lifting the panels is specified by the specialty lifting engineer to provide an adequate factor of safety of about 1.67 against cracking. For most projects, a minimum compressive strength of 2,500 psi with a corresponding allowable flexural stress of 300 psi (typically calculated as 6 ) is specified by the specialty lifting engineer and is considered the minimum requirement prior to lifting the panels.
In some panels with extremely large or unusual openings, external strong-backs will have to be added temporarily to the panel to resist the calculated bending moments and stiffen the panel sufficiently in order to keep the concrete flexural stresses below the estimated cracking strength of the section. The use of strong-backs add time and expense to the project. Many times slightly increasing the thickness of the panels can eliminate the need for strong-backs and actually reduce the cost of the project. Simply adding reinforcing steel has limited effectiveness, especially because the steel remains primarily dormant until the concrete cracks.
The Engineer-of-Record (EOR) for a building typically has limited involvement in the means and methods of rigging and lifting a panel during construction, and the related cracking that could occur. However, the EOR often has more control to address potential cracks associated with concrete drying shrinkage.
Cracking in tilt-up wall panels can occur when excessive restraint prevents the movement from horizontal drying shrinkage. Drying shrinkage naturally occurs as water exits the concrete material, and can become a significant consideration depending upon several factors. Fortunately, vertical panel joints that are free of panel-to-panel connections inherently provide strain relief for the horizontal concrete shrinkage; however, diaphragm chord connections at the roof and floors, and foundation and slab connections, create unintentional restraint. Greater panel widths have greater horizontal shrinkage potential, so limiting widths where possible is recommended. Panel widths between 20 and 30 feet are most common.
When welded panel-to-panel connections occur, isolated embedded plates and anchors near the panel joints could suffer a concrete breakout failure unless sufficient reinforcing steel is utilized to develop the resulting forces deeper into the concrete. Figure 1 illustrates a panel-to-panel connection with bolts in horizontal slotted holes to accommodate the horizontal movement; however, the plate was inadvertently welded on both sides, creating horizontal restraint. Tilt-up designers often avoid welding a large series of panels together across the panel joint to minimize this problem. Roof and floor chord connections are an exception.
At the roof and floor chords, welded connections are common, but the use of horizontally slotted bolt holes near the panel joints in rolled steel ledger sections minimizes the restraint to horizontal shrinkage near the vulnerable panel joint edge. Additionally, some engineers specify a delay in welding the panels together across the joint until roof erection is well underway to allow a larger percentage of the ultimate horizontal shrinkage to occur, and allow the concrete strength to increase, prior to welded restraint. The best solution is to keep restrained panel-to-panel connections well away from panel joints.
Similar restraint issues can occur after the joint below the panel is grouted, or if panels are immediately connected to foundations and/or the slab-on-grade. By delaying connections to the footing or slab and allowing a larger percentage of the ultimate drying shrinkage to occur, while also allowing the concrete strength to increase, the likelihood of developing these cracks is reduced.
It is not practical to expect all restraint to be eliminated, and it may be prudent to provide additional reinforcing to limit crack widths. In many parts of North America, the tilt-up wall panels are placed on cementitious grout pads on top of the foundation, with the resulting joint subsequently grouted, and the only positive connection occurring at the floor slab at some later date during construction. In this situation, providing enough reinforcing steel to withstand the calculated restraint force may be an appropriate course of action to consider, as is demonstrated in the following example:
ChordBot is described as a MIDI chord instrument with a 32 step sequencer and advanced arpeggiator. One of its novel features includes the dedicated chord modifier keys which allow for simple selection of chords to enable you to quickly build songs.
Rounik is the Executive Editor for Ask.Audio & macProVideo. He's built a crack team of professional musicians and writers to create one of the most visited online resources for news, review, tutorials and interviews for modern musician and producer.As an Apple Certified Trainer for Logic Pro Rounik has taught teachers, professional... Read More
@JiggyWig said:Looking for a good app (iPhone & iPad preferably) for experimenting/noodling with chord progressions (especially with simple modulations). MIDI out/export a plus, but probably not a deal breaker.
It seems like we have just given you the same list of apps that are in the store that you had "no idea what to take a crack at." I'm sure all these apps are great, but you can't buy them all. And some may be more than you need. So maybe you could help us by telling us: what do you mean by experimenting/noodling?
Most apps do more than one thing. Some are very simple and some of them are very deep and powerful, like Polychord. Some are awesome if you do electronica and some are better suited if you are a singer/songwriter.
Ever find yourself humming a melody or thinking through a chord progression while on your morning commute, but stuck without an easy way to explore it further? FourTrack is the perfect solution to this debacle. FourTrack is an incredibly powerful app that acts as a fully functional four-track recorder right from your phone. The app boasts a large suite of functions, including multitrack recording (four tracks plus a bounce), flawless graphics and delay compensation, input monitoring, calibrated meters and faders, master FX and EQ, and file import and sharing. Plus, it can record at true 16 bit, 44.1 kHz (CD quality). Inspiration can come in stages, and this app will catch each and every wave of new creative insight that comes to you with impressive quality control and ease of use.
Pads are probably the least expensive and simplest way to fill out the sound of your worship band. We all want our worship bands to have a full sound. But as I worship leader, I know how tough it is to achieve a full sound with your traditional instruments like an acoustic guitar, drums, piano, and bass guitar. Pads fill in the cracks and make your band sound so much more full.
Worship songs come in a variety of keys and chord progressions. A single bundle of pads can work for all of them. One bundle includes 12 keys of music. Since the pads were created to drone over any chord in a given key, it does not matter what chord progression you play. Pads will always sound great.
The new key detection engine builds on the chromagram and expands it with another artificial intelligence unit based around a statistical chord progression model that analysing the chord sequence is able to understand the key of the song, this has the great advantage that the key recognition is always realtime so you can change song without the need to reset the plugin, or if the song changes key in some part of it, the plugin will simply be able to detect the new chord sequence and follow the key change, all of this working just on your DAW, with no need for an internet connection.
The two chromagrams (the one used for chord recognition and the one for key recognition) are shown on the GUI so that you can know which notes are playing and which ones you can use for your track, also we added a handy keyboard display that allows you to see which keys are being played. This is extremely useful if you use SongKey MK4 for acapellas or other samples, with a quick look you can know the key of your samples and which notes to use in your tracks to complement those samples.
Thank you for the demo Saverio:) Fantastic plugin! I am not a musician but a producer and songwriter and this would really speed up the process of finding chords as base to be inspired from for an arrangement. I should definitely try it out. 2ff7e9595c
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